diff --git a/implement/PersistentProcess/PersistentProcess.Test/TestWebHost.cs b/implement/PersistentProcess/PersistentProcess.Test/TestWebHost.cs
index bbcfb8e5..62831c0c 100644
--- a/implement/PersistentProcess/PersistentProcess.Test/TestWebHost.cs
+++ b/implement/PersistentProcess/PersistentProcess.Test/TestWebHost.cs
@@ -1,1067 +1,1067 @@
-using FluentAssertions;
-using Kalmit.PersistentProcess.WebHost;
-using Microsoft.AspNetCore.Builder;
-using Microsoft.AspNetCore.Hosting;
-using Microsoft.AspNetCore.Http;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using MoreLinq;
-using System;
-using System.Collections.Generic;
-using System.Collections.Immutable;
-using System.IO;
-using System.Linq;
-using System.Net;
-using System.Net.Http;
-using System.Net.Http.Headers;
-
-namespace Kalmit.PersistentProcess.Test
-{
-    [TestClass]
-    public class TestWebHost
-    {
-        [TestMethod]
-        public void Web_host_stores_reduction_every_hour()
-        {
-            var persistentProcessHostDateTime = new DateTimeOffset(2018, 11, 4, 8, 17, 13, TimeSpan.Zero);
-
-            void letTimePassInPersistentProcessHost(TimeSpan amount) =>
-                persistentProcessHostDateTime = persistentProcessHostDateTime + amount;
-
-            var allEventsAndExpectedResponses =
-                TestSetup.CounterProcessTestEventsAndExpectedResponses(
-                    new (int addition, int expectedResponse)[]
-                    {
-                        (0, 0),
-                        (1, 1),
-                        (3, 4),
-                        (5, 9),
-                        (7, 16),
-                        (11, 27),
-                        (-13, 14),
-                    }).ToList();
-
-            var eventsAndExpectedResponsesBatches = allEventsAndExpectedResponses.Batch(3).ToList();
-
-            Assert.IsTrue(2 < eventsAndExpectedResponsesBatches.Count, "More than two batches of events to test with.");
-
-            using (var testSetup = WebHostTestSetup.Setup(
-                TestElmWebAppHttpServer.CounterWebApp, () => persistentProcessHostDateTime))
-            {
-                IEnumerable<string> ReadStoredReductionFileRelativePaths()
-                {
-                    System.Threading.Thread.Sleep(1111);  //  Storing reduction may be completed after client has received response.
-                    return testSetup.BuildProcessStoreInFileDirectory().ReductionsFilesNames();
-                }
-
-                using (var server = testSetup.BuildServer())
-                {
-                    //  Do not depend on an exact number of reductions stored on initialization: Send one request before measuring the number of stored reductions.
-                    using (var client = server.CreateClient())
-                    {
-                        var httpResponse =
-                            client.PostAsync("", new StringContent("", System.Text.Encoding.UTF8)).Result;
-
-                        var httpResponseContent = httpResponse.Content.ReadAsStringAsync().Result;
-                    }
-
-                    foreach (var eventsAndExpectedResponsesBatch in eventsAndExpectedResponsesBatches)
-                    {
-                        var beforeBatchStoredReductionsCount = ReadStoredReductionFileRelativePaths().Count();
-
-                        letTimePassInPersistentProcessHost(TimeSpan.FromHours(1));
-
-                        foreach (var (serializedEvent, expectedResponse) in eventsAndExpectedResponsesBatch)
-                        {
-                            letTimePassInPersistentProcessHost(TimeSpan.FromSeconds(4));
-
-                            using (var client = server.CreateClient())
-                            {
-                                var httpResponse =
-                                    client.PostAsync("", new StringContent(serializedEvent, System.Text.Encoding.UTF8)).Result;
-
-                                var httpResponseContent = httpResponse.Content.ReadAsStringAsync().Result;
-
-                                Assert.AreEqual(expectedResponse, httpResponseContent, false, "server response");
-                            }
-
-                            Assert.AreEqual(
-                                beforeBatchStoredReductionsCount + 1,
-                                ReadStoredReductionFileRelativePaths().Count(),
-                                "Number of stored reductions has increased by one since previous batch.");
-                        }
-                    }
-                }
-            }
-        }
-
-        [TestMethod]
-        public void Web_host_continues_composition_log_on_new_file_every_calendar_day()
-        {
-            var persistentProcessHostDateTime = new DateTimeOffset(2018, 11, 4, 8, 17, 13, TimeSpan.Zero);
-
-            void letTimePassInPersistentProcessHost(TimeSpan amount) =>
-                persistentProcessHostDateTime = persistentProcessHostDateTime + amount;
-
-            var allEventsAndExpectedResponses =
-                TestSetup.CounterProcessTestEventsAndExpectedResponses(
-                    new (int addition, int expectedResponse)[]
-                    {
-                        (0, 0),
-                        (1, 1),
-                        (3, 4),
-                        (5, 9),
-                        (7, 16),
-                        (11, 27),
-                        (-13, 14),
-                    }).ToList();
-
-            var eventsAndExpectedResponsesBatches = allEventsAndExpectedResponses.Batch(3).ToList();
-
-            Assert.IsTrue(2 < eventsAndExpectedResponsesBatches.Count, "More than two batches of events to test with.");
-
-            using (var testSetup = WebHostTestSetup.Setup(
-                TestElmWebAppHttpServer.CounterWebApp, () => persistentProcessHostDateTime))
-            {
-                ProcessStore.ProcessStoreInFileDirectory BuildProcessStore() =>
-                    testSetup.BuildProcessStoreInFileDirectory();
-
-                IEnumerable<string> ReadCompositionLogFilesNames() =>
-                    BuildProcessStore().EnumerateCompositionsLogFilesPaths()
-                    .Select(filePath => String.Join(Path.DirectorySeparatorChar, filePath));
-
-                string FirstReductionRecordFile = null;
-
-                void deleteAllReductionRecordFilesExceptTheFirstOne()
-                {
-                    var filesNamesExceptTheFirst =
-                        BuildProcessStore().ReductionsFilesNames().Except(new[] { FirstReductionRecordFile }).ToList();
-
-                    filesNamesExceptTheFirst.ForEach(reductionFileName =>
-                    {
-                        foreach (var matchingFile in Directory.EnumerateFiles(
-                            testSetup.ProcessStoreDirectory, reductionFileName, SearchOption.AllDirectories))
-                            File.Delete(matchingFile);
-                    });
-
-                    Assert.IsTrue(BuildProcessStore().ReductionsFilesNames().Count() <= 1);
-                }
-
-                string PostStringContentAndGetResponseStringFromServer(
-                    Microsoft.AspNetCore.TestHost.TestServer server, string requestContent)
-                {
-                    try
-                    {
-                        using (var client = server.CreateClient())
-                        {
-                            var httpResponse =
-                                client.PostAsync("", new StringContent(requestContent, System.Text.Encoding.UTF8)).Result;
-
-                            return httpResponse.Content.ReadAsStringAsync().Result;
-                        }
-                    }
-                    finally
-                    {
-                        FirstReductionRecordFile =
-                            FirstReductionRecordFile ?? BuildProcessStore().ReductionsFilesNames().FirstOrDefault();
-                    }
-                }
-
-                using (var server = testSetup.BuildServer())
-                {
-                    //  Do not depend on an exact number of files stored on initialization: Send one request before measuring the number of stored files.
-                    PostStringContentAndGetResponseStringFromServer(server, "");
-                }
-
-                foreach (var eventsAndExpectedResponsesBatch in eventsAndExpectedResponsesBatches)
-                {
-                    var beforeBatchCompositionLogFiles = ReadCompositionLogFilesNames().ToList();
-
-                    letTimePassInPersistentProcessHost(TimeSpan.FromDays(1));
-
-                    var batchDayCompositionLogFileNameExpectedStart =
-                        persistentProcessHostDateTime.ToString("yyyy-MM-dd");
-
-                    //  Test that restoring works over all composition log files.
-                    deleteAllReductionRecordFilesExceptTheFirstOne();
-
-                    using (var server = testSetup.BuildServer())
-                    {
-                        foreach (var (serializedEvent, expectedResponse) in eventsAndExpectedResponsesBatch)
-                        {
-                            letTimePassInPersistentProcessHost(TimeSpan.FromMinutes(4));
-
-                            var httpResponseContent = PostStringContentAndGetResponseStringFromServer(server, serializedEvent);
-
-                            Assert.AreEqual(expectedResponse, httpResponseContent, false, "server response");
-
-                            var inBatchNewCompositionLogFiles =
-                                ReadCompositionLogFilesNames().Except(beforeBatchCompositionLogFiles).ToList();
-
-                            Assert.AreEqual(
-                                1,
-                                inBatchNewCompositionLogFiles.Count,
-                                "Exactly one new composition log files since start of batch.");
-
-                            var newCompositionLogFileName = Path.GetFileName(inBatchNewCompositionLogFiles.Single());
-
-                            Assert.IsTrue(
-                                newCompositionLogFileName.StartsWith(batchDayCompositionLogFileNameExpectedStart),
-                                "File name of new composition log file ('" + newCompositionLogFileName +
-                                "') starts with '" + batchDayCompositionLogFileNameExpectedStart + "')");
-                        }
-                    }
-                }
-            }
-        }
-
-        [TestMethod]
-        public void Web_host_serves_static_files_besides_hosting_persistent_process()
-        {
-            var defaultStaticFile =
-                Enumerable.Range(0, 10_000).SelectMany(elem => BitConverter.GetBytes((UInt16)elem))
-                .Concat(System.Text.Encoding.UTF8.GetBytes("Default static file content from String\nAnother line"))
-                .Concat(Enumerable.Range(0, 100_000).SelectMany(elem => BitConverter.GetBytes((UInt16)elem)))
-                .ToArray();
-
-            var defaultStaticFileInSubdirectory = System.Text.Encoding.UTF8.GetBytes("Default static file in 'subdirectory/'.");
-
-            const string processEventPath = "process-event";
-
-            var webAppConfig =
-                TestElmWebAppHttpServer.CounterWebApp
-                .WithJsonStructure(
-                    new WebAppConfigurationJsonStructure
-                    {
-                        mapsFromRequestUrlToStaticFileName = new[]
-                        {
-                            new WebAppConfigurationJsonStructure.ConditionalMapFromStringToString
-                            {
-                                matchingRegexPattern = "^.+/subdirectory/(.+)$",
-                                resultString = nameof(defaultStaticFileInSubdirectory),
-                            },
-                            new WebAppConfigurationJsonStructure.ConditionalMapFromStringToString
-                            {
-                                matchingRegexPattern = "^(?!.+/" + processEventPath + "$).*",
-                                resultString = nameof(defaultStaticFile),
-                            },
-                        },
-                    })
-                .WithStaticFiles(
-                    new[]
-                    {
-                        ((IImmutableList<string>)ImmutableList.Create(nameof(defaultStaticFile)), (IImmutableList<byte>)defaultStaticFile.ToImmutableList()),
-                        (ImmutableList.Create(nameof(defaultStaticFileInSubdirectory)), defaultStaticFileInSubdirectory.ToImmutableList()),
-                    });
-
-            var allEventsAndExpectedResponses =
-                TestSetup.CounterProcessTestEventsAndExpectedResponses(
-                    new (int addition, int expectedResponse)[]
-                    {
-                        (0, 0),
-                        (1, 1),
-                        (3, 4),
-                        (5, 9),
-                        (7, 16),
-                        (11, 27),
-                        (-13, 14),
-                    }).ToList();
-
-            using (var testSetup = WebHostTestSetup.Setup(webAppConfig))
-            {
-                string PostAppEventAndGetResponseStringFromServer(
-                    Microsoft.AspNetCore.TestHost.TestServer server, string appEvent)
-                {
-                    using (var client = server.CreateClient())
-                    {
-                        var httpResponse =
-                            client.PostAsync(processEventPath, new StringContent(appEvent, System.Text.Encoding.UTF8)).Result;
-
-                        return httpResponse.Content.ReadAsStringAsync().Result;
-                    }
-                }
-
-                using (var server = testSetup.BuildServer())
-                {
-                    using (var client = server.CreateClient())
-                    {
-                        void assertHttpResponseForStaticFile(string path, byte[] expectedFile)
-                        {
-                            try
-                            {
-                                var httpResponse = client.GetAsync(path).Result;
-
-                                Assert.AreEqual(HttpStatusCode.OK, httpResponse.StatusCode, "HTTP GET response status code.");
-
-                                var responseContent = httpResponse.Content.ReadAsByteArrayAsync().Result;
-
-                                CollectionAssert.AreEqual(expectedFile, responseContent, "HTTP GET response content.");
-
-                                Assert.AreEqual(
-                                    HttpStatusCode.MethodNotAllowed,
-                                    client.PostAsync(path, new StringContent("")).Result.StatusCode,
-                                    "HTTP POST response status code.");
-
-                                Assert.AreEqual(
-                                    HttpStatusCode.MethodNotAllowed,
-                                    client.PutAsync(path, new StringContent("")).Result.StatusCode,
-                                    "HTTP PUT response status code.");
-                            }
-                            catch (Exception e)
-                            {
-                                throw new Exception("Failed for static file at path '" + path + "'", e);
-                            }
-                        }
-
-                        Assert.ThrowsException<Exception>(
-                            () => assertHttpResponseForStaticFile(
-                                "", System.Text.Encoding.UTF8.GetBytes("This should not match")));
-
-                        foreach (var pathWhichShouldBeMappedToDefaultStaticFile in new[] { "", "index.html", "almost-anything-else-too" })
-                        {
-                            assertHttpResponseForStaticFile(
-                                pathWhichShouldBeMappedToDefaultStaticFile, defaultStaticFile);
-                        }
-
-                        foreach (var pathWhichShouldBeMappedToDefaultStaticFile in new[] { "subdirectory/a-path", "subdirectory/another-path" })
-                        {
-                            assertHttpResponseForStaticFile(
-                                pathWhichShouldBeMappedToDefaultStaticFile, defaultStaticFileInSubdirectory);
-                        }
-                    }
-
-                    foreach (var (serializedEvent, expectedResponse) in allEventsAndExpectedResponses)
-                    {
-                        var httpResponseContent = PostAppEventAndGetResponseStringFromServer(server, serializedEvent);
-
-                        Assert.AreEqual(expectedResponse, httpResponseContent, false, "server response");
-                    }
-                }
-            }
-        }
-
-        [TestMethod]
-        public void Web_host_can_be_configured_to_serve_static_files_without_elm_app()
-        {
-            var defaultStaticFile =
-                Enumerable.Range(0, 10_000).SelectMany(elem => BitConverter.GetBytes((UInt16)elem))
-                .Concat(System.Text.Encoding.UTF8.GetBytes("Default static file content from String\nAnother line"))
-                .Concat(Enumerable.Range(0, 100_000).SelectMany(elem => BitConverter.GetBytes((UInt16)elem)))
-                .ToArray();
-
-            var webAppConfig =
-                new WebAppConfiguration()
-                .WithJsonStructure(
-                    new WebAppConfigurationJsonStructure
-                    {
-                        mapsFromRequestUrlToStaticFileName = new[]
-                        {
-                            new WebAppConfigurationJsonStructure.ConditionalMapFromStringToString
-                            {
-                                matchingRegexPattern = ".*",
-                                resultString = nameof(defaultStaticFile),
-                            },
-                        },
-                    })
-                .WithStaticFiles(
-                    new[]
-                    {
-                        ((IImmutableList<string>)ImmutableList.Create(nameof(defaultStaticFile)), (IImmutableList<byte>)defaultStaticFile.ToImmutableList()),
-                    });
-
-            using (var testSetup = WebHostTestSetup.Setup(webAppConfig))
-            {
-                using (var server = testSetup.BuildServer())
-                {
-                    using (var client = server.CreateClient())
-                    {
-                        foreach (var pathWhichShouldBeMappedToDefaultStaticFile in new[] { "", "index.html", "almost-anything-else-too" })
-                        {
-                            var response = client.GetAsync(pathWhichShouldBeMappedToDefaultStaticFile).Result;
-
-                            Assert.AreEqual(HttpStatusCode.OK, response.StatusCode, "Response status code");
-                            CollectionAssert.AreEqual(
-                                defaultStaticFile,
-                                response.Content.ReadAsByteArrayAsync().Result,
-                                "Response Content");
-                        }
-                    }
-                }
-            }
-        }
-
-        [TestMethod]
-        public void Web_host_rate_limits_requests_before_reaching_persistent_process()
-        {
-            const int requestBatchSize = 100;
-            const int minimumNumberOfRequestsInFastBatchExpectedToBeBlockedByRateLimit = 85;
-            const int rateLimitWindowSize = 10;
-
-            var persistentProcessHostDateTime = new DateTimeOffset(2018, 11, 12, 19, 51, 13, TimeSpan.Zero);
-
-            void letTimePassInPersistentProcessHost(TimeSpan amount) =>
-                persistentProcessHostDateTime = persistentProcessHostDateTime + amount;
-
-            var requestsBatches =
-                Enumerable.Range(0, 3)
-                .Select(batchIndex =>
-                    Enumerable.Range(0, requestBatchSize)
-                    .Select(indexInBatch => "Batch " + batchIndex + ", Event " + indexInBatch).ToList())
-                    .ToList();
-
-            var webAppConfig =
-                TestElmWebAppHttpServer.CounterWebApp
-                .WithJsonStructure(
-                    new WebAppConfigurationJsonStructure
-                    {
-                        singleRateLimitWindowPerClientIPv4Address = new WebAppConfigurationJsonStructure.RateLimitWindow
-                        {
-                            windowSizeInMs = 1000 * rateLimitWindowSize,
-                            limit = rateLimitWindowSize,
-                        },
-                    });
-
-            using (var testSetup = WebHostTestSetup.Setup(webAppConfig, () => persistentProcessHostDateTime))
-            {
-                IEnumerable<string> EnumerateStoredProcessEventsHttpRequestsBodies() =>
-                    testSetup.EnumerateStoredProcessEventsReverse()
-                    .Select(processEvent => processEvent?.httpRequest?.request?.bodyAsString)
-                    .WhereNotNull();
-
-                HttpResponseMessage PostStringContentToServer(
-                    Microsoft.AspNetCore.TestHost.TestServer server, string requestContent)
-                {
-                    using (var client = server.CreateClient())
-                    {
-                        return
-                            client.PostAsync("", new StringContent(requestContent, System.Text.Encoding.UTF8)).Result;
-                    }
-                }
-
-                IEnumerable<HttpResponseMessage> whereStatusCodeTooManyRequests(
-                    IEnumerable<HttpResponseMessage> httpResponses) =>
-                    httpResponses.Where(httpResponse => httpResponse.StatusCode == HttpStatusCode.TooManyRequests);
-
-                using (var server = testSetup.BuildServer())
-                {
-                    {
-                        var firstBatchHttpResponses =
-                            requestsBatches[0].Select(processEvent =>
-                            {
-                                letTimePassInPersistentProcessHost(TimeSpan.FromSeconds(1));
-
-                                return PostStringContentToServer(server, processEvent);
-                            }).ToList();
-
-                        whereStatusCodeTooManyRequests(firstBatchHttpResponses).Count()
-                        .Should().Be(0, "No HTTP response from the first batch has status code 'Too Many Requests'.");
-
-                        CollectionAssert.IsSubsetOf(
-                            requestsBatches[0],
-                            EnumerateStoredProcessEventsHttpRequestsBodies().ToList(),
-                            "All events from the first batch have been stored.");
-                    }
-
-                    {
-                        var secondBatchHttpResponses =
-                            requestsBatches[1].Select(processEvent =>
-                            {
-                                //  Process the events in the second batch in smaller timespan so that effect of the rate-limit should be observable.
-                                letTimePassInPersistentProcessHost(TimeSpan.FromSeconds(0.1));
-
-                                return PostStringContentToServer(server, processEvent);
-                            }).ToList();
-
-                        whereStatusCodeTooManyRequests(secondBatchHttpResponses).Count()
-                        .Should().BeGreaterThan(minimumNumberOfRequestsInFastBatchExpectedToBeBlockedByRateLimit,
-                            "At least this many requests in the fast batch are expected to be answered with status code 'Too Many Requests'.");
-
-                        requestsBatches[1].Except(EnumerateStoredProcessEventsHttpRequestsBodies()).Count()
-                        .Should().BeGreaterThan(minimumNumberOfRequestsInFastBatchExpectedToBeBlockedByRateLimit,
-                            "At least this many requests in the fast batch are expected to be filtered out by rate-limit before reaching the persistent process.");
-                    }
-
-                    {
-                        letTimePassInPersistentProcessHost(TimeSpan.FromSeconds(rateLimitWindowSize));
-
-                        var thirdBatchHttpResponses =
-                            requestsBatches[2].Select(processEvent =>
-                            {
-                                letTimePassInPersistentProcessHost(TimeSpan.FromSeconds(1));
-
-                                return PostStringContentToServer(server, processEvent);
-                            }).ToList();
-
-                        whereStatusCodeTooManyRequests(thirdBatchHttpResponses).Count()
-                        .Should().Be(0, "No HTTP response from the third batch has status code 'Too Many Requests'.");
-
-                        CollectionAssert.IsSubsetOf(
-                            requestsBatches[2],
-                            EnumerateStoredProcessEventsHttpRequestsBodies().ToList(),
-                            "All events from the third batch have been stored.");
-                    }
-                }
-            }
-        }
-
-        [TestMethod]
-        public void Web_host_supports_setting_persistent_process_state_only_after_authorization()
-        {
-            const string rootPassword = "Root-Password_1234567";
-
-            Func<IWebHostBuilder, IWebHostBuilder> webHostBuilderMap =
-                builder => builder.WithSettingAdminRootPassword(rootPassword);
-
-            using (var testSetup = WebHostTestSetup.Setup(TestElmWebAppHttpServer.StringBuilderWebApp, webHostBuilderMap))
-            {
-                using (var server = testSetup.BuildServer())
-                {
-                    Assert.AreEqual(
-                        "",
-                        HttpGetAtRoot(server).Content.ReadAsStringAsync().Result,
-                        "Initial State");
-
-                    Assert.AreEqual(HttpStatusCode.OK, HttpPostStringContentAtRoot(server, "part-a").StatusCode);
-
-                    Assert.AreEqual(HttpStatusCode.OK, HttpPostStringContentAtRoot(server, "-part-b").StatusCode);
-
-                    Assert.AreEqual(
-                        "part-a-part-b",
-                        HttpGetAtRoot(server).Content.ReadAsStringAsync().Result,
-                        "State After Multiple Posts");
-
-                    using (var client = server.CreateClient())
-                    {
-                        Assert.AreEqual(
-                            HttpStatusCode.Unauthorized,
-                            HttpSetPersistentProcessState(client, "new-state").Result.StatusCode,
-                                "HTTP status code for unauthorized request to set persistent process state.");
-
-                        Assert.AreEqual(
-                            "part-a-part-b",
-                            HttpGetAtRoot(server).Content.ReadAsStringAsync().Result,
-                            "State after failing to set persistent process state.");
-
-                        client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(
-                            "Basic",
-                            Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(
-                                WebHost.Configuration.BasicAuthenticationForAdminRoot(rootPassword))));
-
-                        Assert.AreEqual(
-                            HttpStatusCode.OK,
-                            HttpSetPersistentProcessState(client, @"""new-state""").Result.StatusCode,
-                                "HTTP status code for authorized request to set persistent process state.");
-                    }
-
-                    Assert.AreEqual(
-                        "new-state",
-                        HttpGetAtRoot(server).Content.ReadAsStringAsync().Result,
-                        "State after setting persistent process state.");
-
-                    Assert.AreEqual(HttpStatusCode.OK, HttpPostStringContentAtRoot(server, "_appendix").StatusCode);
-                }
-
-                using (var server = testSetup.BuildServer())
-                {
-                    Assert.AreEqual(
-                        "new-state_appendix",
-                        HttpGetAtRoot(server).Content.ReadAsStringAsync().Result,
-                        "State after setting persistent process state, appending, and restarting server.");
-                }
-            }
-        }
-
-        [TestMethod]
-        public void Web_host_propagates_HTTP_headers()
-        {
-            // This name needs to be consistent with the code in Elm app CrossPropagateHttpHeadersToAndFromBody.
-            const string appSpecificHttpResponseHeaderName = "response-header-name";
-
-            using (var testSetup = WebHostTestSetup.Setup(TestElmWebAppHttpServer.CrossPropagateHttpHeadersToAndFromBody, builder => builder))
-            {
-                using (var server = testSetup.BuildServer())
-                {
-                    using (var client = server.CreateClient())
-                    {
-                        var requestHeaderValue = "HTTP request header value.";
-                        var requestContentString = "HTTP request content.";
-
-                        const string appSpecificHttpRequestHeaderName = "request-header-name";
-
-                        client.DefaultRequestHeaders.Add(appSpecificHttpRequestHeaderName, WebUtility.UrlEncode(requestHeaderValue));
-
-                        var response = client.PostAsync("", new StringContent(requestContentString)).Result;
-
-                        Assert.AreEqual("application/json", response.Content.Headers.ContentType.ToString());
-
-                        var responseContentString = response.Content.ReadAsStringAsync().Result;
-
-                        var collectionFromResponseContent =
-                            Newtonsoft.Json.JsonConvert.DeserializeObject<Web_host_propagates_HTTP_headers_Response_Entry[]>(
-                                responseContentString);
-
-                        var matchingEntryFromResponseContent =
-                            collectionFromResponseContent
-                            .First(entry => entry.name == appSpecificHttpRequestHeaderName);
-
-                        Assert.AreEqual(
-                            requestHeaderValue,
-                            WebUtility.UrlDecode(matchingEntryFromResponseContent.values.FirstOrDefault()),
-                            "Expect the HTTP request header was propagated to an entry in the response content.");
-
-                        response.Headers.TryGetValues(appSpecificHttpResponseHeaderName, out var appSpecificHttpHeaderValues);
-
-                        Assert.AreEqual(
-                            requestContentString,
-                            WebUtility.UrlDecode(appSpecificHttpHeaderValues?.FirstOrDefault()),
-                            "Expect the HTTP request content was propagated to the response header with name '" + appSpecificHttpResponseHeaderName + "'");
-                    }
-                }
-            }
-        }
-
-        [TestMethod]
-        public void Host_supports_sending_HTTP_requests()
-        {
-            const string echoServerUrl = "http://localhost:6789/";
-
-            var echoWebHostBuilder =
-                Microsoft.AspNetCore.WebHost.CreateDefaultBuilder()
-                .Configure(app =>
-                {
-                    app.Run(async (context) =>
-                    {
-                        var requestRecord = Asp.AsPersistentProcessInterfaceHttpRequest(context.Request);
-
-                        context.Response.StatusCode = 200;
-
-                        await context.Response.WriteAsync(Newtonsoft.Json.JsonConvert.SerializeObject(requestRecord));
-                    });
-                })
-                .UseUrls(echoServerUrl);
-
-            using (var echoServer = echoWebHostBuilder.Build())
-            {
-                echoServer.Start();
-
-                using (var testSetup = WebHostTestSetup.Setup(TestElmWebAppHttpServer.HttpProxyWebApp, builder => builder))
-                {
-                    using (var server = testSetup.BuildServer())
-                    {
-                        using (var client = server.CreateClient())
-                        {
-                            var customHeaderName = "My-custom-header";
-                            var customHeaderValue = "Hello!";
-                            var requestContentString = "HTTP request content.";
-
-                            var httpRequestMessage = new HttpRequestMessage(new HttpMethod("post"), "")
-                            {
-                                Content = new StringContent(requestContentString),
-                            };
-
-                            httpRequestMessage.Headers.Add("forward-to", echoServerUrl);
-
-                            httpRequestMessage.Headers.Add(customHeaderName, customHeaderValue);
-
-                            var response = client.SendAsync(httpRequestMessage).Result;
-
-                            var responseContentString = response.Content.ReadAsStringAsync().Result;
-
-                            var echoRequestStructure =
-                                Newtonsoft.Json.JsonConvert.DeserializeObject<InterfaceToHost.HttpRequest>(responseContentString);
-
-                            Assert.AreEqual(
-                                requestContentString,
-                                echoRequestStructure.bodyAsString,
-                                "Request body is propagated.");
-
-                            var echoCustomHeaderValues =
-                                echoRequestStructure.headers
-                                .FirstOrDefault(header => header.name == customHeaderName)
-                                ?.values;
-
-                            Assert.AreEqual(
-                                1,
-                                echoCustomHeaderValues?.Length,
-                                "Custom header name is propagated.");
-
-                            Assert.AreEqual(
-                                customHeaderValue,
-                                echoCustomHeaderValues[0],
-                                "Custom header value is propagated.");
-                        }
-
-                        using (var client = server.CreateClient())
-                        {
-                            var contentTypeHeaderName = "content-type";
-                            var customContentType = "application/octet-stream";
-
-                            var httpRequestMessage = new HttpRequestMessage(new HttpMethod("post"), "")
-                            {
-                                Content = new ByteArrayContent(System.Text.Encoding.UTF8.GetBytes("Hello!")),
-                            };
-
-                            httpRequestMessage.Content.Headers.ContentType = new MediaTypeHeaderValue(customContentType);
-
-                            httpRequestMessage.Headers.Add("forward-to", echoServerUrl);
-
-                            var response = client.SendAsync(httpRequestMessage).Result;
-
-                            var responseContentString = response.Content.ReadAsStringAsync().Result;
-
-                            var echoRequestStructure =
-                                Newtonsoft.Json.JsonConvert.DeserializeObject<InterfaceToHost.HttpRequest>(responseContentString);
-
-                            var observedContentType =
-                                echoRequestStructure.headers
-                                .SingleOrDefault(header => string.Equals(header.name, contentTypeHeaderName, StringComparison.InvariantCultureIgnoreCase))
-                                ?.values.SingleOrDefault();
-
-                            Assert.AreEqual(
-                                customContentType,
-                                observedContentType,
-                                "Sent HTTP request with content type '" + customContentType + "'.");
-                        }
-                    }
-                }
-            }
-        }
-
-        [TestMethod]
-        public void Web_host_sends_HTTP_response_only_after_write_to_history()
-        {
-            using (var testSetup = WebHostTestSetup.Setup(TestElmWebAppHttpServer.CounterWebApp))
-            {
-                async System.Threading.Tasks.Task<HttpResponseMessage> PostStringContentToServer(
-                    Microsoft.AspNetCore.TestHost.TestServer server, string requestContent)
-                {
-                    using (var client = server.CreateClient())
-                    {
-                        return await
-                            client.PostAsync("", new StringContent(requestContent, System.Text.Encoding.UTF8));
-                    }
-                }
-
-                Action runBeforeMutateInFileStore = null;
-
-                using (var server = testSetup.BuildServer(
-                    processStoreFileStoreMap: originalFileStore =>
-                    {
-                        return new FileStoreFromDelegates(
-                            setFileContent: new Action<IImmutableList<string>, byte[]>((path, fileContent) =>
-                            {
-                                runBeforeMutateInFileStore?.Invoke();
-                                originalFileStore.SetFileContent(path, fileContent);
-                            }),
-                            appendFileContent: new Action<IImmutableList<string>, byte[]>((path, fileContent) =>
-                            {
-                                runBeforeMutateInFileStore?.Invoke();
-                                originalFileStore.AppendFileContent(path, fileContent);
-                            }),
-                            deleteFile: new Action<IImmutableList<string>>(path =>
-                            {
-                                runBeforeMutateInFileStore?.Invoke();
-                                originalFileStore.DeleteFile(path);
-                            }),
-                            getFileContent: originalFileStore.GetFileContent,
-                            listFilesInDirectory: originalFileStore.ListFilesInDirectory);
-                    }))
-                {
-                    var delayMutateInFileStore = false;
-
-                    runBeforeMutateInFileStore = new Action(() =>
-                    {
-                        while (!delayMutateInFileStore)
-                        {
-                            System.Threading.Tasks.Task.Delay(11).Wait();
-                        }
-                    });
-
-                    var httpPostTask = PostStringContentToServer(server, "");
-
-                    System.Threading.Tasks.Task.Delay(4000).Wait();
-
-                    Assert.IsFalse(httpPostTask.IsCompleted, "HTTP task is not completed.");
-
-                    delayMutateInFileStore = true;
-
-                    System.Threading.Tasks.Task.Delay(1000).Wait();
-
-                    Assert.IsTrue(httpPostTask.IsCompleted, "HTTP task is completed.");
-                }
-            }
-        }
-
-        [TestMethod]
-        public void Web_host_supporting_migrations_supports_set_app_config()
-        {
-            const string rootPassword = "Root-Password_1234567";
-
-            var allEventsAndExpectedResponses =
-                TestSetup.CounterProcessTestEventsAndExpectedResponses(
-                    new (int addition, int expectedResponse)[]
-                    {
-                        (0, 0),
-                        (1, 1),
-                        (3, 4),
-                        (5, 9),
-                        (7, 16),
-                        (11, 27),
-                        (-13, 14),
-                    }).ToList();
-
-            var eventsAndExpectedResponsesBatches = allEventsAndExpectedResponses.Batch(3).ToList();
-
-            Assert.IsTrue(2 < eventsAndExpectedResponsesBatches.Count, "More than two batches of events to test with.");
-
-            var webAppConfigZipArchive = ZipArchive.ZipArchiveFromEntries(
-                TestElmWebAppHttpServer.CounterWebApp.AsFiles());
-
-            Func<IWebHostBuilder, IWebHostBuilder> webHostBuilderMap =
-                builder => builder.WithSettingAdminRootPassword(rootPassword);
-
-            HttpClient createClientWithAuthorizationHeader(Microsoft.AspNetCore.TestHost.TestServer server)
-            {
-                var adminClient = server.CreateClient();
-
-                adminClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(
-                    "Basic",
-                    Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(
-                        WebHost.Configuration.BasicAuthenticationForAdminRoot(rootPassword))));
-
-                return adminClient;
-            }
-
-            using (var testSetup = WebHostSupportingMigrationsTestSetup.Setup(webHostBuilderMap))
-            {
-                using (var server = testSetup.BuildServer())
-                {
-                    using (var adminClient = createClientWithAuthorizationHeader(server))
-                    {
-                        var setAppConfigResponse = adminClient.PostAsync(
-                            StartupSupportingMigrations.PathApiSetAppConfigAndInitState,
-                            new ByteArrayContent(webAppConfigZipArchive)).Result;
-
-                        Assert.IsTrue(setAppConfigResponse.IsSuccessStatusCode, "set-app response IsSuccessStatusCode");
-                    }
-
-                    using (var adminClient = createClientWithAuthorizationHeader(server))
-                    {
-                        var getAppConfigResponse = adminClient.GetAsync(StartupSupportingMigrations.PathApiGetAppConfig).Result;
-
-                        Assert.IsTrue(getAppConfigResponse.IsSuccessStatusCode, "get-app response IsSuccessStatusCode");
-
-                        var getAppResponseContent = getAppConfigResponse.Content.ReadAsByteArrayAsync().Result;
-
-                        CollectionAssert.AreEqual(webAppConfigZipArchive, getAppResponseContent, "Get the same configuration file back.");
-                    }
-
-                    foreach (var (serializedEvent, expectedResponse) in eventsAndExpectedResponsesBatches.First())
-                    {
-                        using (var client = testSetup.BuildPublicAppHttpClient())
-                        {
-                            var httpResponse =
-                                client.PostAsync("", new StringContent(serializedEvent, System.Text.Encoding.UTF8)).Result;
-
-                            var httpResponseContent = httpResponse.Content.ReadAsStringAsync().Result;
-
-                            Assert.AreEqual(expectedResponse, httpResponseContent, false, "server response matches " + expectedResponse);
-                        }
-                    }
-
-                    using (var adminClient = createClientWithAuthorizationHeader(server))
-                    {
-                        var setAppHttpResponse = adminClient.PostAsync(
-                            StartupSupportingMigrations.PathApiSetAppConfigAndInitState,
-                            new ByteArrayContent(webAppConfigZipArchive)).Result;
-                    }
-                }
-
-                foreach (var eventsAndExpectedResponsesBatch in eventsAndExpectedResponsesBatches)
-                {
-                    using (var server = testSetup.BuildServer())
-                    {
-                        using (var adminClient = createClientWithAuthorizationHeader(server))
-                        {
-                            var setAppHttpResponse = adminClient.PostAsync(
-                                StartupSupportingMigrations.PathApiSetAppConfigAndContinueState,
-                                new ByteArrayContent(webAppConfigZipArchive)).Result;
-
-                            Assert.IsTrue(setAppHttpResponse.IsSuccessStatusCode, "set-app response IsSuccessStatusCode");
-                        }
-
-                        foreach (var (serializedEvent, expectedResponse) in eventsAndExpectedResponsesBatch)
-                        {
-                            using (var client = testSetup.BuildPublicAppHttpClient())
-                            {
-                                var httpResponse =
-                                    client.PostAsync("", new StringContent(serializedEvent, System.Text.Encoding.UTF8)).Result;
-
-                                var httpResponseContent = httpResponse.Content.ReadAsStringAsync().Result;
-
-                                Assert.AreEqual(expectedResponse, httpResponseContent, false, "server response matches " + expectedResponse);
-                            }
-                        }
-                    }
-                }
-            }
-        }
-
-
-        [TestMethod]
-        public void Web_host_supporting_migrations_supports_migrate_elm_state()
-        {
-            const string rootPassword = "Root-Password_1234567";
-
-            var webAppConfigZipArchive = ZipArchive.ZipArchiveFromEntries(
-                TestElmWebAppHttpServer.StringBuilderWebApp.AsFiles());
-
-            var migrateElmAppZipArchive = ZipArchive.ZipArchiveFromEntries(
-                TestSetup.GetElmAppFromExampleName("migrate-string-append-length"));
-
-            Func<IWebHostBuilder, IWebHostBuilder> webHostBuilderMap =
-                builder => builder.WithSettingAdminRootPassword(rootPassword);
-
-            HttpClient createClientWithAuthorizationHeader(Microsoft.AspNetCore.TestHost.TestServer server)
-            {
-                var adminClient = server.CreateClient();
-
-                adminClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(
-                    "Basic",
-                    Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(
-                        WebHost.Configuration.BasicAuthenticationForAdminRoot(rootPassword))));
-
-                return adminClient;
-            }
-
-            using (var testSetup = WebHostSupportingMigrationsTestSetup.Setup(webHostBuilderMap))
-            {
-                using (var server = testSetup.BuildServer())
-                {
-                    using (var adminClient = createClientWithAuthorizationHeader(server))
-                    {
-                        var setAppConfigResponse = adminClient.PostAsync(
-                            StartupSupportingMigrations.PathApiSetAppConfigAndInitState,
-                            new ByteArrayContent(webAppConfigZipArchive)).Result;
-
-                        Assert.IsTrue(setAppConfigResponse.IsSuccessStatusCode, "set-app response IsSuccessStatusCode");
-                    }
-
-                    using (var client = testSetup.BuildPublicAppHttpClient())
-                    {
-                        var httpResponse =
-                            client.PostAsync("", new StringContent("a", System.Text.Encoding.UTF8)).Result;
-
-                        var httpResponseContent = httpResponse.Content.ReadAsStringAsync().Result;
-
-                        Assert.AreEqual("a", httpResponseContent, false, "Server response content.");
-                    }
-
-                    using (var client = testSetup.BuildPublicAppHttpClient())
-                    {
-                        var httpResponse =
-                            client.PostAsync("", new StringContent("b", System.Text.Encoding.UTF8)).Result;
-
-                        var httpResponseContent = httpResponse.Content.ReadAsStringAsync().Result;
-
-                        Assert.AreEqual("ab", httpResponseContent, false, "Server response content.");
-                    }
-
-                    using (var adminClient = createClientWithAuthorizationHeader(server))
-                    {
-                        var migrateHttpResponse = adminClient.PostAsync(
-                            StartupSupportingMigrations.PathApiMigrateElmState,
-                            new ByteArrayContent(migrateElmAppZipArchive)).Result;
-
-                        Assert.IsTrue(migrateHttpResponse.IsSuccessStatusCode, "migrate-elm-state response IsSuccessStatusCode");
-                    }
-
-                    using (var client = testSetup.BuildPublicAppHttpClient())
-                    {
-                        var httpResponse =
-                            client.PostAsync("", new StringContent("c", System.Text.Encoding.UTF8)).Result;
-
-                        var httpResponseContent = httpResponse.Content.ReadAsStringAsync().Result;
-
-                        Assert.AreEqual("ab2c", httpResponseContent, false, "Server response content.");
-                    }
-                }
-            }
-        }
-
-        class FileStoreFromDelegates : IFileStore
-        {
-            readonly Action<IImmutableList<string>, byte[]> setFileContent;
-
-            readonly Action<IImmutableList<string>, byte[]> appendFileContent;
-
-            readonly Action<IImmutableList<string>> deleteFile;
-
-            readonly Func<IImmutableList<string>, byte[]> getFileContent;
-
-            readonly Func<IImmutableList<string>, IEnumerable<IImmutableList<string>>> listFilesInDirectory;
-
-            public FileStoreFromDelegates(
-                Action<IImmutableList<string>, byte[]> setFileContent,
-                Action<IImmutableList<string>, byte[]> appendFileContent,
-                 Action<IImmutableList<string>> deleteFile,
-                Func<IImmutableList<string>, byte[]> getFileContent,
-                Func<IImmutableList<string>, IEnumerable<IImmutableList<string>>> listFilesInDirectory)
-            {
-                this.setFileContent = setFileContent;
-                this.appendFileContent = appendFileContent;
-                this.deleteFile = deleteFile;
-                this.getFileContent = getFileContent;
-                this.listFilesInDirectory = listFilesInDirectory;
-            }
-
-            public void AppendFileContent(IImmutableList<string> path, byte[] fileContent) =>
-                appendFileContent(path, fileContent);
-
-            public void DeleteFile(IImmutableList<string> path) =>
-                deleteFile(path);
-
-            public byte[] GetFileContent(IImmutableList<string> path) =>
-                getFileContent(path);
-
-            public IEnumerable<IImmutableList<string>> ListFilesInDirectory(IImmutableList<string> directoryPath) =>
-                listFilesInDirectory(directoryPath);
-
-            public void SetFileContent(IImmutableList<string> path, byte[] fileContent) =>
-                setFileContent(path, fileContent);
-        }
-
-        class Web_host_propagates_HTTP_headers_Response_Entry
-        {
-            public string name = null;
-
-            public string[] values = null;
-        }
-
-        static HttpResponseMessage HttpGetAtRoot(
-            Microsoft.AspNetCore.TestHost.TestServer server)
-        {
-            using (var client = server.CreateClient())
-            {
-                return client.GetAsync("").Result;
-            }
-        }
-
-        static HttpResponseMessage HttpPostStringContentAtRoot(
-            Microsoft.AspNetCore.TestHost.TestServer server, string requestContent)
-        {
-            using (var client = server.CreateClient())
-            {
-                return
-                    client.PostAsync("", new StringContent(requestContent, System.Text.Encoding.UTF8)).Result;
-            }
-        }
-
-        static System.Threading.Tasks.Task<HttpResponseMessage> HttpSetPersistentProcessState(
-            HttpClient client,
-            string state) =>
-            client.PostAsync(
-                Kalmit.PersistentProcess.WebHost.Configuration.AdminPath +
-                Kalmit.PersistentProcess.WebHost.Configuration.ApiPersistentProcessStatePath,
-                new StringContent(state, System.Text.Encoding.UTF8));
-    }
+using FluentAssertions;
+using Kalmit.PersistentProcess.WebHost;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Http;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MoreLinq;
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.IO;
+using System.Linq;
+using System.Net;
+using System.Net.Http;
+using System.Net.Http.Headers;
+
+namespace Kalmit.PersistentProcess.Test
+{
+    [TestClass]
+    public class TestWebHost
+    {
+        [TestMethod]
+        public void Web_host_stores_reduction_every_hour()
+        {
+            var persistentProcessHostDateTime = new DateTimeOffset(2018, 11, 4, 8, 17, 13, TimeSpan.Zero);
+
+            void letTimePassInPersistentProcessHost(TimeSpan amount) =>
+                persistentProcessHostDateTime = persistentProcessHostDateTime + amount;
+
+            var allEventsAndExpectedResponses =
+                TestSetup.CounterProcessTestEventsAndExpectedResponses(
+                    new (int addition, int expectedResponse)[]
+                    {
+                        (0, 0),
+                        (1, 1),
+                        (3, 4),
+                        (5, 9),
+                        (7, 16),
+                        (11, 27),
+                        (-13, 14),
+                    }).ToList();
+
+            var eventsAndExpectedResponsesBatches = allEventsAndExpectedResponses.Batch(3).ToList();
+
+            Assert.IsTrue(2 < eventsAndExpectedResponsesBatches.Count, "More than two batches of events to test with.");
+
+            using (var testSetup = WebHostTestSetup.Setup(
+                TestElmWebAppHttpServer.CounterWebApp, () => persistentProcessHostDateTime))
+            {
+                IEnumerable<string> ReadStoredReductionFileRelativePaths()
+                {
+                    System.Threading.Thread.Sleep(1111);  //  Storing reduction may be completed after client has received response.
+                    return testSetup.BuildProcessStoreInFileDirectory().ReductionsFilesNames();
+                }
+
+                using (var server = testSetup.BuildServer())
+                {
+                    //  Do not depend on an exact number of reductions stored on initialization: Send one request before measuring the number of stored reductions.
+                    using (var client = server.CreateClient())
+                    {
+                        var httpResponse =
+                            client.PostAsync("", new StringContent("", System.Text.Encoding.UTF8)).Result;
+
+                        var httpResponseContent = httpResponse.Content.ReadAsStringAsync().Result;
+                    }
+
+                    foreach (var eventsAndExpectedResponsesBatch in eventsAndExpectedResponsesBatches)
+                    {
+                        var beforeBatchStoredReductionsCount = ReadStoredReductionFileRelativePaths().Count();
+
+                        letTimePassInPersistentProcessHost(TimeSpan.FromHours(1));
+
+                        foreach (var (serializedEvent, expectedResponse) in eventsAndExpectedResponsesBatch)
+                        {
+                            letTimePassInPersistentProcessHost(TimeSpan.FromSeconds(4));
+
+                            using (var client = server.CreateClient())
+                            {
+                                var httpResponse =
+                                    client.PostAsync("", new StringContent(serializedEvent, System.Text.Encoding.UTF8)).Result;
+
+                                var httpResponseContent = httpResponse.Content.ReadAsStringAsync().Result;
+
+                                Assert.AreEqual(expectedResponse, httpResponseContent, false, "server response");
+                            }
+
+                            Assert.AreEqual(
+                                beforeBatchStoredReductionsCount + 1,
+                                ReadStoredReductionFileRelativePaths().Count(),
+                                "Number of stored reductions has increased by one since previous batch.");
+                        }
+                    }
+                }
+            }
+        }
+
+        [TestMethod]
+        public void Web_host_continues_composition_log_on_new_file_every_calendar_day()
+        {
+            var persistentProcessHostDateTime = new DateTimeOffset(2018, 11, 4, 8, 17, 13, TimeSpan.Zero);
+
+            void letTimePassInPersistentProcessHost(TimeSpan amount) =>
+                persistentProcessHostDateTime = persistentProcessHostDateTime + amount;
+
+            var allEventsAndExpectedResponses =
+                TestSetup.CounterProcessTestEventsAndExpectedResponses(
+                    new (int addition, int expectedResponse)[]
+                    {
+                        (0, 0),
+                        (1, 1),
+                        (3, 4),
+                        (5, 9),
+                        (7, 16),
+                        (11, 27),
+                        (-13, 14),
+                    }).ToList();
+
+            var eventsAndExpectedResponsesBatches = allEventsAndExpectedResponses.Batch(3).ToList();
+
+            Assert.IsTrue(2 < eventsAndExpectedResponsesBatches.Count, "More than two batches of events to test with.");
+
+            using (var testSetup = WebHostTestSetup.Setup(
+                TestElmWebAppHttpServer.CounterWebApp, () => persistentProcessHostDateTime))
+            {
+                ProcessStore.ProcessStoreInFileDirectory BuildProcessStore() =>
+                    testSetup.BuildProcessStoreInFileDirectory();
+
+                IEnumerable<string> ReadCompositionLogFilesNames() =>
+                    BuildProcessStore().EnumerateCompositionsLogFilesPaths()
+                    .Select(filePath => String.Join(Path.DirectorySeparatorChar, filePath));
+
+                string FirstReductionRecordFile = null;
+
+                void deleteAllReductionRecordFilesExceptTheFirstOne()
+                {
+                    var filesNamesExceptTheFirst =
+                        BuildProcessStore().ReductionsFilesNames().Except(new[] { FirstReductionRecordFile }).ToList();
+
+                    filesNamesExceptTheFirst.ForEach(reductionFileName =>
+                    {
+                        foreach (var matchingFile in Directory.EnumerateFiles(
+                            testSetup.ProcessStoreDirectory, reductionFileName, SearchOption.AllDirectories))
+                            File.Delete(matchingFile);
+                    });
+
+                    Assert.IsTrue(BuildProcessStore().ReductionsFilesNames().Count() <= 1);
+                }
+
+                string PostStringContentAndGetResponseStringFromServer(
+                    Microsoft.AspNetCore.TestHost.TestServer server, string requestContent)
+                {
+                    try
+                    {
+                        using (var client = server.CreateClient())
+                        {
+                            var httpResponse =
+                                client.PostAsync("", new StringContent(requestContent, System.Text.Encoding.UTF8)).Result;
+
+                            return httpResponse.Content.ReadAsStringAsync().Result;
+                        }
+                    }
+                    finally
+                    {
+                        FirstReductionRecordFile =
+                            FirstReductionRecordFile ?? BuildProcessStore().ReductionsFilesNames().FirstOrDefault();
+                    }
+                }
+
+                using (var server = testSetup.BuildServer())
+                {
+                    //  Do not depend on an exact number of files stored on initialization: Send one request before measuring the number of stored files.
+                    PostStringContentAndGetResponseStringFromServer(server, "");
+                }
+
+                foreach (var eventsAndExpectedResponsesBatch in eventsAndExpectedResponsesBatches)
+                {
+                    var beforeBatchCompositionLogFiles = ReadCompositionLogFilesNames().ToList();
+
+                    letTimePassInPersistentProcessHost(TimeSpan.FromDays(1));
+
+                    var batchDayCompositionLogFileNameExpectedStart =
+                        persistentProcessHostDateTime.ToString("yyyy-MM-dd");
+
+                    //  Test that restoring works over all composition log files.
+                    deleteAllReductionRecordFilesExceptTheFirstOne();
+
+                    using (var server = testSetup.BuildServer())
+                    {
+                        foreach (var (serializedEvent, expectedResponse) in eventsAndExpectedResponsesBatch)
+                        {
+                            letTimePassInPersistentProcessHost(TimeSpan.FromMinutes(4));
+
+                            var httpResponseContent = PostStringContentAndGetResponseStringFromServer(server, serializedEvent);
+
+                            Assert.AreEqual(expectedResponse, httpResponseContent, false, "server response");
+
+                            var inBatchNewCompositionLogFiles =
+                                ReadCompositionLogFilesNames().Except(beforeBatchCompositionLogFiles).ToList();
+
+                            Assert.AreEqual(
+                                1,
+                                inBatchNewCompositionLogFiles.Count,
+                                "Exactly one new composition log files since start of batch.");
+
+                            var newCompositionLogFileName = Path.GetFileName(inBatchNewCompositionLogFiles.Single());
+
+                            Assert.IsTrue(
+                                newCompositionLogFileName.StartsWith(batchDayCompositionLogFileNameExpectedStart),
+                                "File name of new composition log file ('" + newCompositionLogFileName +
+                                "') starts with '" + batchDayCompositionLogFileNameExpectedStart + "')");
+                        }
+                    }
+                }
+            }
+        }
+
+        [TestMethod]
+        public void Web_host_serves_static_files_besides_hosting_persistent_process()
+        {
+            var defaultStaticFile =
+                Enumerable.Range(0, 10_000).SelectMany(elem => BitConverter.GetBytes((UInt16)elem))
+                .Concat(System.Text.Encoding.UTF8.GetBytes("Default static file content from String\nAnother line"))
+                .Concat(Enumerable.Range(0, 100_000).SelectMany(elem => BitConverter.GetBytes((UInt16)elem)))
+                .ToArray();
+
+            var defaultStaticFileInSubdirectory = System.Text.Encoding.UTF8.GetBytes("Default static file in 'subdirectory/'.");
+
+            const string processEventPath = "process-event";
+
+            var webAppConfig =
+                TestElmWebAppHttpServer.CounterWebApp
+                .WithJsonStructure(
+                    new WebAppConfigurationJsonStructure
+                    {
+                        mapsFromRequestUrlToStaticFileName = new[]
+                        {
+                            new WebAppConfigurationJsonStructure.ConditionalMapFromStringToString
+                            {
+                                matchingRegexPattern = "^.+/subdirectory/(.+)$",
+                                resultString = nameof(defaultStaticFileInSubdirectory),
+                            },
+                            new WebAppConfigurationJsonStructure.ConditionalMapFromStringToString
+                            {
+                                matchingRegexPattern = "^(?!.+/" + processEventPath + "$).*",
+                                resultString = nameof(defaultStaticFile),
+                            },
+                        },
+                    })
+                .WithStaticFiles(
+                    new[]
+                    {
+                        ((IImmutableList<string>)ImmutableList.Create(nameof(defaultStaticFile)), (IImmutableList<byte>)defaultStaticFile.ToImmutableList()),
+                        (ImmutableList.Create(nameof(defaultStaticFileInSubdirectory)), defaultStaticFileInSubdirectory.ToImmutableList()),
+                    });
+
+            var allEventsAndExpectedResponses =
+                TestSetup.CounterProcessTestEventsAndExpectedResponses(
+                    new (int addition, int expectedResponse)[]
+                    {
+                        (0, 0),
+                        (1, 1),
+                        (3, 4),
+                        (5, 9),
+                        (7, 16),
+                        (11, 27),
+                        (-13, 14),
+                    }).ToList();
+
+            using (var testSetup = WebHostTestSetup.Setup(webAppConfig))
+            {
+                string PostAppEventAndGetResponseStringFromServer(
+                    Microsoft.AspNetCore.TestHost.TestServer server, string appEvent)
+                {
+                    using (var client = server.CreateClient())
+                    {
+                        var httpResponse =
+                            client.PostAsync(processEventPath, new StringContent(appEvent, System.Text.Encoding.UTF8)).Result;
+
+                        return httpResponse.Content.ReadAsStringAsync().Result;
+                    }
+                }
+
+                using (var server = testSetup.BuildServer())
+                {
+                    using (var client = server.CreateClient())
+                    {
+                        void assertHttpResponseForStaticFile(string path, byte[] expectedFile)
+                        {
+                            try
+                            {
+                                var httpResponse = client.GetAsync(path).Result;
+
+                                Assert.AreEqual(HttpStatusCode.OK, httpResponse.StatusCode, "HTTP GET response status code.");
+
+                                var responseContent = httpResponse.Content.ReadAsByteArrayAsync().Result;
+
+                                CollectionAssert.AreEqual(expectedFile, responseContent, "HTTP GET response content.");
+
+                                Assert.AreEqual(
+                                    HttpStatusCode.MethodNotAllowed,
+                                    client.PostAsync(path, new StringContent("")).Result.StatusCode,
+                                    "HTTP POST response status code.");
+
+                                Assert.AreEqual(
+                                    HttpStatusCode.MethodNotAllowed,
+                                    client.PutAsync(path, new StringContent("")).Result.StatusCode,
+                                    "HTTP PUT response status code.");
+                            }
+                            catch (Exception e)
+                            {
+                                throw new Exception("Failed for static file at path '" + path + "'", e);
+                            }
+                        }
+
+                        Assert.ThrowsException<Exception>(
+                            () => assertHttpResponseForStaticFile(
+                                "", System.Text.Encoding.UTF8.GetBytes("This should not match")));
+
+                        foreach (var pathWhichShouldBeMappedToDefaultStaticFile in new[] { "", "index.html", "almost-anything-else-too" })
+                        {
+                            assertHttpResponseForStaticFile(
+                                pathWhichShouldBeMappedToDefaultStaticFile, defaultStaticFile);
+                        }
+
+                        foreach (var pathWhichShouldBeMappedToDefaultStaticFile in new[] { "subdirectory/a-path", "subdirectory/another-path" })
+                        {
+                            assertHttpResponseForStaticFile(
+                                pathWhichShouldBeMappedToDefaultStaticFile, defaultStaticFileInSubdirectory);
+                        }
+                    }
+
+                    foreach (var (serializedEvent, expectedResponse) in allEventsAndExpectedResponses)
+                    {
+                        var httpResponseContent = PostAppEventAndGetResponseStringFromServer(server, serializedEvent);
+
+                        Assert.AreEqual(expectedResponse, httpResponseContent, false, "server response");
+                    }
+                }
+            }
+        }
+
+        [TestMethod]
+        public void Web_host_can_be_configured_to_serve_static_files_without_elm_app()
+        {
+            var defaultStaticFile =
+                Enumerable.Range(0, 10_000).SelectMany(elem => BitConverter.GetBytes((UInt16)elem))
+                .Concat(System.Text.Encoding.UTF8.GetBytes("Default static file content from String\nAnother line"))
+                .Concat(Enumerable.Range(0, 100_000).SelectMany(elem => BitConverter.GetBytes((UInt16)elem)))
+                .ToArray();
+
+            var webAppConfig =
+                new WebAppConfiguration()
+                .WithJsonStructure(
+                    new WebAppConfigurationJsonStructure
+                    {
+                        mapsFromRequestUrlToStaticFileName = new[]
+                        {
+                            new WebAppConfigurationJsonStructure.ConditionalMapFromStringToString
+                            {
+                                matchingRegexPattern = ".*",
+                                resultString = nameof(defaultStaticFile),
+                            },
+                        },
+                    })
+                .WithStaticFiles(
+                    new[]
+                    {
+                        ((IImmutableList<string>)ImmutableList.Create(nameof(defaultStaticFile)), (IImmutableList<byte>)defaultStaticFile.ToImmutableList()),
+                    });
+
+            using (var testSetup = WebHostTestSetup.Setup(webAppConfig))
+            {
+                using (var server = testSetup.BuildServer())
+                {
+                    using (var client = server.CreateClient())
+                    {
+                        foreach (var pathWhichShouldBeMappedToDefaultStaticFile in new[] { "", "index.html", "almost-anything-else-too" })
+                        {
+                            var response = client.GetAsync(pathWhichShouldBeMappedToDefaultStaticFile).Result;
+
+                            Assert.AreEqual(HttpStatusCode.OK, response.StatusCode, "Response status code");
+                            CollectionAssert.AreEqual(
+                                defaultStaticFile,
+                                response.Content.ReadAsByteArrayAsync().Result,
+                                "Response Content");
+                        }
+                    }
+                }
+            }
+        }
+
+        [TestMethod]
+        public void Web_host_rate_limits_requests_before_reaching_persistent_process()
+        {
+            const int requestBatchSize = 100;
+            const int minimumNumberOfRequestsInFastBatchExpectedToBeBlockedByRateLimit = 85;
+            const int rateLimitWindowSize = 10;
+
+            var persistentProcessHostDateTime = new DateTimeOffset(2018, 11, 12, 19, 51, 13, TimeSpan.Zero);
+
+            void letTimePassInPersistentProcessHost(TimeSpan amount) =>
+                persistentProcessHostDateTime = persistentProcessHostDateTime + amount;
+
+            var requestsBatches =
+                Enumerable.Range(0, 3)
+                .Select(batchIndex =>
+                    Enumerable.Range(0, requestBatchSize)
+                    .Select(indexInBatch => "Batch " + batchIndex + ", Event " + indexInBatch).ToList())
+                    .ToList();
+
+            var webAppConfig =
+                TestElmWebAppHttpServer.CounterWebApp
+                .WithJsonStructure(
+                    new WebAppConfigurationJsonStructure
+                    {
+                        singleRateLimitWindowPerClientIPv4Address = new WebAppConfigurationJsonStructure.RateLimitWindow
+                        {
+                            windowSizeInMs = 1000 * rateLimitWindowSize,
+                            limit = rateLimitWindowSize,
+                        },
+                    });
+
+            using (var testSetup = WebHostTestSetup.Setup(webAppConfig, () => persistentProcessHostDateTime))
+            {
+                IEnumerable<string> EnumerateStoredProcessEventsHttpRequestsBodies() =>
+                    testSetup.EnumerateStoredProcessEventsReverse()
+                    .Select(processEvent => processEvent?.httpRequest?.request?.bodyAsString)
+                    .WhereNotNull();
+
+                HttpResponseMessage PostStringContentToServer(
+                    Microsoft.AspNetCore.TestHost.TestServer server, string requestContent)
+                {
+                    using (var client = server.CreateClient())
+                    {
+                        return
+                            client.PostAsync("", new StringContent(requestContent, System.Text.Encoding.UTF8)).Result;
+                    }
+                }
+
+                IEnumerable<HttpResponseMessage> whereStatusCodeTooManyRequests(
+                    IEnumerable<HttpResponseMessage> httpResponses) =>
+                    httpResponses.Where(httpResponse => httpResponse.StatusCode == HttpStatusCode.TooManyRequests);
+
+                using (var server = testSetup.BuildServer())
+                {
+                    {
+                        var firstBatchHttpResponses =
+                            requestsBatches[0].Select(processEvent =>
+                            {
+                                letTimePassInPersistentProcessHost(TimeSpan.FromSeconds(1));
+
+                                return PostStringContentToServer(server, processEvent);
+                            }).ToList();
+
+                        whereStatusCodeTooManyRequests(firstBatchHttpResponses).Count()
+                        .Should().Be(0, "No HTTP response from the first batch has status code 'Too Many Requests'.");
+
+                        CollectionAssert.IsSubsetOf(
+                            requestsBatches[0],
+                            EnumerateStoredProcessEventsHttpRequestsBodies().ToList(),
+                            "All events from the first batch have been stored.");
+                    }
+
+                    {
+                        var secondBatchHttpResponses =
+                            requestsBatches[1].Select(processEvent =>
+                            {
+                                //  Process the events in the second batch in smaller timespan so that effect of the rate-limit should be observable.
+                                letTimePassInPersistentProcessHost(TimeSpan.FromSeconds(0.1));
+
+                                return PostStringContentToServer(server, processEvent);
+                            }).ToList();
+
+                        whereStatusCodeTooManyRequests(secondBatchHttpResponses).Count()
+                        .Should().BeGreaterThan(minimumNumberOfRequestsInFastBatchExpectedToBeBlockedByRateLimit,
+                            "At least this many requests in the fast batch are expected to be answered with status code 'Too Many Requests'.");
+
+                        requestsBatches[1].Except(EnumerateStoredProcessEventsHttpRequestsBodies()).Count()
+                        .Should().BeGreaterThan(minimumNumberOfRequestsInFastBatchExpectedToBeBlockedByRateLimit,
+                            "At least this many requests in the fast batch are expected to be filtered out by rate-limit before reaching the persistent process.");
+                    }
+
+                    {
+                        letTimePassInPersistentProcessHost(TimeSpan.FromSeconds(rateLimitWindowSize));
+
+                        var thirdBatchHttpResponses =
+                            requestsBatches[2].Select(processEvent =>
+                            {
+                                letTimePassInPersistentProcessHost(TimeSpan.FromSeconds(1));
+
+                                return PostStringContentToServer(server, processEvent);
+                            }).ToList();
+
+                        whereStatusCodeTooManyRequests(thirdBatchHttpResponses).Count()
+                        .Should().Be(0, "No HTTP response from the third batch has status code 'Too Many Requests'.");
+
+                        CollectionAssert.IsSubsetOf(
+                            requestsBatches[2],
+                            EnumerateStoredProcessEventsHttpRequestsBodies().ToList(),
+                            "All events from the third batch have been stored.");
+                    }
+                }
+            }
+        }
+
+        [TestMethod]
+        public void Web_host_supports_setting_persistent_process_state_only_after_authorization()
+        {
+            const string rootPassword = "Root-Password_1234567";
+
+            Func<IWebHostBuilder, IWebHostBuilder> webHostBuilderMap =
+                builder => builder.WithSettingAdminRootPassword(rootPassword);
+
+            using (var testSetup = WebHostTestSetup.Setup(TestElmWebAppHttpServer.StringBuilderWebApp, webHostBuilderMap))
+            {
+                using (var server = testSetup.BuildServer())
+                {
+                    Assert.AreEqual(
+                        "",
+                        HttpGetAtRoot(server).Content.ReadAsStringAsync().Result,
+                        "Initial State");
+
+                    Assert.AreEqual(HttpStatusCode.OK, HttpPostStringContentAtRoot(server, "part-a").StatusCode);
+
+                    Assert.AreEqual(HttpStatusCode.OK, HttpPostStringContentAtRoot(server, "-part-b").StatusCode);
+
+                    Assert.AreEqual(
+                        "part-a-part-b",
+                        HttpGetAtRoot(server).Content.ReadAsStringAsync().Result,
+                        "State After Multiple Posts");
+
+                    using (var client = server.CreateClient())
+                    {
+                        Assert.AreEqual(
+                            HttpStatusCode.Unauthorized,
+                            HttpSetPersistentProcessState(client, "new-state").Result.StatusCode,
+                                "HTTP status code for unauthorized request to set persistent process state.");
+
+                        Assert.AreEqual(
+                            "part-a-part-b",
+                            HttpGetAtRoot(server).Content.ReadAsStringAsync().Result,
+                            "State after failing to set persistent process state.");
+
+                        client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(
+                            "Basic",
+                            Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(
+                                WebHost.Configuration.BasicAuthenticationForAdminRoot(rootPassword))));
+
+                        Assert.AreEqual(
+                            HttpStatusCode.OK,
+                            HttpSetPersistentProcessState(client, @"""new-state""").Result.StatusCode,
+                                "HTTP status code for authorized request to set persistent process state.");
+                    }
+
+                    Assert.AreEqual(
+                        "new-state",
+                        HttpGetAtRoot(server).Content.ReadAsStringAsync().Result,
+                        "State after setting persistent process state.");
+
+                    Assert.AreEqual(HttpStatusCode.OK, HttpPostStringContentAtRoot(server, "_appendix").StatusCode);
+                }
+
+                using (var server = testSetup.BuildServer())
+                {
+                    Assert.AreEqual(
+                        "new-state_appendix",
+                        HttpGetAtRoot(server).Content.ReadAsStringAsync().Result,
+                        "State after setting persistent process state, appending, and restarting server.");
+                }
+            }
+        }
+
+        [TestMethod]
+        public void Web_host_propagates_HTTP_headers()
+        {
+            // This name needs to be consistent with the code in Elm app CrossPropagateHttpHeadersToAndFromBody.
+            const string appSpecificHttpResponseHeaderName = "response-header-name";
+
+            using (var testSetup = WebHostTestSetup.Setup(TestElmWebAppHttpServer.CrossPropagateHttpHeadersToAndFromBody, builder => builder))
+            {
+                using (var server = testSetup.BuildServer())
+                {
+                    using (var client = server.CreateClient())
+                    {
+                        var requestHeaderValue = "HTTP request header value.";
+                        var requestContentString = "HTTP request content.";
+
+                        const string appSpecificHttpRequestHeaderName = "request-header-name";
+
+                        client.DefaultRequestHeaders.Add(appSpecificHttpRequestHeaderName, WebUtility.UrlEncode(requestHeaderValue));
+
+                        var response = client.PostAsync("", new StringContent(requestContentString)).Result;
+
+                        Assert.AreEqual("application/json", response.Content.Headers.ContentType.ToString());
+
+                        var responseContentString = response.Content.ReadAsStringAsync().Result;
+
+                        var collectionFromResponseContent =
+                            Newtonsoft.Json.JsonConvert.DeserializeObject<Web_host_propagates_HTTP_headers_Response_Entry[]>(
+                                responseContentString);
+
+                        var matchingEntryFromResponseContent =
+                            collectionFromResponseContent
+                            .First(entry => entry.name == appSpecificHttpRequestHeaderName);
+
+                        Assert.AreEqual(
+                            requestHeaderValue,
+                            WebUtility.UrlDecode(matchingEntryFromResponseContent.values.FirstOrDefault()),
+                            "Expect the HTTP request header was propagated to an entry in the response content.");
+
+                        response.Headers.TryGetValues(appSpecificHttpResponseHeaderName, out var appSpecificHttpHeaderValues);
+
+                        Assert.AreEqual(
+                            requestContentString,
+                            WebUtility.UrlDecode(appSpecificHttpHeaderValues?.FirstOrDefault()),
+                            "Expect the HTTP request content was propagated to the response header with name '" + appSpecificHttpResponseHeaderName + "'");
+                    }
+                }
+            }
+        }
+
+        [TestMethod]
+        public void Host_supports_sending_HTTP_requests()
+        {
+            const string echoServerUrl = "http://localhost:6789/";
+
+            var echoWebHostBuilder =
+                Microsoft.AspNetCore.WebHost.CreateDefaultBuilder()
+                .Configure(app =>
+                {
+                    app.Run(async (context) =>
+                    {
+                        var requestRecord = Asp.AsPersistentProcessInterfaceHttpRequest(context.Request);
+
+                        context.Response.StatusCode = 200;
+
+                        await context.Response.WriteAsync(Newtonsoft.Json.JsonConvert.SerializeObject(requestRecord));
+                    });
+                })
+                .UseUrls(echoServerUrl);
+
+            using (var echoServer = echoWebHostBuilder.Build())
+            {
+                echoServer.Start();
+
+                using (var testSetup = WebHostTestSetup.Setup(TestElmWebAppHttpServer.HttpProxyWebApp, builder => builder))
+                {
+                    using (var server = testSetup.BuildServer())
+                    {
+                        using (var client = server.CreateClient())
+                        {
+                            var customHeaderName = "My-custom-header";
+                            var customHeaderValue = "Hello!";
+                            var requestContentString = "HTTP request content.";
+
+                            var httpRequestMessage = new HttpRequestMessage(new HttpMethod("post"), "")
+                            {
+                                Content = new StringContent(requestContentString),
+                            };
+
+                            httpRequestMessage.Headers.Add("forward-to", echoServerUrl);
+
+                            httpRequestMessage.Headers.Add(customHeaderName, customHeaderValue);
+
+                            var response = client.SendAsync(httpRequestMessage).Result;
+
+                            var responseContentString = response.Content.ReadAsStringAsync().Result;
+
+                            var echoRequestStructure =
+                                Newtonsoft.Json.JsonConvert.DeserializeObject<InterfaceToHost.HttpRequest>(responseContentString);
+
+                            Assert.AreEqual(
+                                requestContentString,
+                                echoRequestStructure.bodyAsString,
+                                "Request body is propagated.");
+
+                            var echoCustomHeaderValues =
+                                echoRequestStructure.headers
+                                .FirstOrDefault(header => header.name == customHeaderName)
+                                ?.values;
+
+                            Assert.AreEqual(
+                                1,
+                                echoCustomHeaderValues?.Length,
+                                "Custom header name is propagated.");
+
+                            Assert.AreEqual(
+                                customHeaderValue,
+                                echoCustomHeaderValues[0],
+                                "Custom header value is propagated.");
+                        }
+
+                        using (var client = server.CreateClient())
+                        {
+                            var contentTypeHeaderName = "content-type";
+                            var customContentType = "application/octet-stream";
+
+                            var httpRequestMessage = new HttpRequestMessage(new HttpMethod("post"), "")
+                            {
+                                Content = new ByteArrayContent(System.Text.Encoding.UTF8.GetBytes("Hello!")),
+                            };
+
+                            httpRequestMessage.Content.Headers.ContentType = new MediaTypeHeaderValue(customContentType);
+
+                            httpRequestMessage.Headers.Add("forward-to", echoServerUrl);
+
+                            var response = client.SendAsync(httpRequestMessage).Result;
+
+                            var responseContentString = response.Content.ReadAsStringAsync().Result;
+
+                            var echoRequestStructure =
+                                Newtonsoft.Json.JsonConvert.DeserializeObject<InterfaceToHost.HttpRequest>(responseContentString);
+
+                            var observedContentType =
+                                echoRequestStructure.headers
+                                .SingleOrDefault(header => string.Equals(header.name, contentTypeHeaderName, StringComparison.InvariantCultureIgnoreCase))
+                                ?.values.SingleOrDefault();
+
+                            Assert.AreEqual(
+                                customContentType,
+                                observedContentType,
+                                "Sent HTTP request with content type '" + customContentType + "'.");
+                        }
+                    }
+                }
+            }
+        }
+
+        [TestMethod]
+        public void Web_host_sends_HTTP_response_only_after_write_to_history()
+        {
+            using (var testSetup = WebHostTestSetup.Setup(TestElmWebAppHttpServer.CounterWebApp))
+            {
+                async System.Threading.Tasks.Task<HttpResponseMessage> PostStringContentToServer(
+                    Microsoft.AspNetCore.TestHost.TestServer server, string requestContent)
+                {
+                    using (var client = server.CreateClient())
+                    {
+                        return await
+                            client.PostAsync("", new StringContent(requestContent, System.Text.Encoding.UTF8));
+                    }
+                }
+
+                Action runBeforeMutateInFileStore = null;
+
+                using (var server = testSetup.BuildServer(
+                    processStoreFileStoreMap: originalFileStore =>
+                    {
+                        return new FileStoreFromDelegates(
+                            setFileContent: new Action<IImmutableList<string>, byte[]>((path, fileContent) =>
+                            {
+                                runBeforeMutateInFileStore?.Invoke();
+                                originalFileStore.SetFileContent(path, fileContent);
+                            }),
+                            appendFileContent: new Action<IImmutableList<string>, byte[]>((path, fileContent) =>
+                            {
+                                runBeforeMutateInFileStore?.Invoke();
+                                originalFileStore.AppendFileContent(path, fileContent);
+                            }),
+                            deleteFile: new Action<IImmutableList<string>>(path =>
+                            {
+                                runBeforeMutateInFileStore?.Invoke();
+                                originalFileStore.DeleteFile(path);
+                            }),
+                            getFileContent: originalFileStore.GetFileContent,
+                            listFilesInDirectory: originalFileStore.ListFilesInDirectory);
+                    }))
+                {
+                    var delayMutateInFileStore = false;
+
+                    runBeforeMutateInFileStore = new Action(() =>
+                    {
+                        while (!delayMutateInFileStore)
+                        {
+                            System.Threading.Tasks.Task.Delay(11).Wait();
+                        }
+                    });
+
+                    var httpPostTask = PostStringContentToServer(server, "");
+
+                    System.Threading.Tasks.Task.Delay(4000).Wait();
+
+                    Assert.IsFalse(httpPostTask.IsCompleted, "HTTP task is not completed.");
+
+                    delayMutateInFileStore = true;
+
+                    System.Threading.Tasks.Task.Delay(1000).Wait();
+
+                    Assert.IsTrue(httpPostTask.IsCompleted, "HTTP task is completed.");
+                }
+            }
+        }
+
+        [TestMethod]
+        public void Web_host_supporting_migrations_supports_set_app_config()
+        {
+            const string rootPassword = "Root-Password_1234567";
+
+            var allEventsAndExpectedResponses =
+                TestSetup.CounterProcessTestEventsAndExpectedResponses(
+                    new (int addition, int expectedResponse)[]
+                    {
+                        (0, 0),
+                        (1, 1),
+                        (3, 4),
+                        (5, 9),
+                        (7, 16),
+                        (11, 27),
+                        (-13, 14),
+                    }).ToList();
+
+            var eventsAndExpectedResponsesBatches = allEventsAndExpectedResponses.Batch(3).ToList();
+
+            Assert.IsTrue(2 < eventsAndExpectedResponsesBatches.Count, "More than two batches of events to test with.");
+
+            var webAppConfigZipArchive = ZipArchive.ZipArchiveFromEntries(
+                TestElmWebAppHttpServer.CounterWebApp.AsFiles());
+
+            Func<IWebHostBuilder, IWebHostBuilder> webHostBuilderMap =
+                builder => builder.WithSettingAdminRootPassword(rootPassword);
+
+            HttpClient createClientWithAuthorizationHeader(Microsoft.AspNetCore.TestHost.TestServer server)
+            {
+                var adminClient = server.CreateClient();
+
+                adminClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(
+                    "Basic",
+                    Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(
+                        WebHost.Configuration.BasicAuthenticationForAdminRoot(rootPassword))));
+
+                return adminClient;
+            }
+
+            using (var testSetup = WebHostSupportingMigrationsTestSetup.Setup(webHostBuilderMap))
+            {
+                using (var server = testSetup.BuildServer())
+                {
+                    using (var adminClient = createClientWithAuthorizationHeader(server))
+                    {
+                        var setAppConfigResponse = adminClient.PostAsync(
+                            StartupSupportingMigrations.PathApiSetAppConfigAndInitState,
+                            new ByteArrayContent(webAppConfigZipArchive)).Result;
+
+                        Assert.IsTrue(setAppConfigResponse.IsSuccessStatusCode, "set-app response IsSuccessStatusCode");
+                    }
+
+                    using (var adminClient = createClientWithAuthorizationHeader(server))
+                    {
+                        var getAppConfigResponse = adminClient.GetAsync(StartupSupportingMigrations.PathApiGetAppConfig).Result;
+
+                        Assert.IsTrue(getAppConfigResponse.IsSuccessStatusCode, "get-app response IsSuccessStatusCode");
+
+                        var getAppResponseContent = getAppConfigResponse.Content.ReadAsByteArrayAsync().Result;
+
+                        CollectionAssert.AreEqual(webAppConfigZipArchive, getAppResponseContent, "Get the same configuration file back.");
+                    }
+
+                    foreach (var (serializedEvent, expectedResponse) in eventsAndExpectedResponsesBatches.First())
+                    {
+                        using (var client = testSetup.BuildPublicAppHttpClient())
+                        {
+                            var httpResponse =
+                                client.PostAsync("", new StringContent(serializedEvent, System.Text.Encoding.UTF8)).Result;
+
+                            var httpResponseContent = httpResponse.Content.ReadAsStringAsync().Result;
+
+                            Assert.AreEqual(expectedResponse, httpResponseContent, false, "server response matches " + expectedResponse);
+                        }
+                    }
+
+                    using (var adminClient = createClientWithAuthorizationHeader(server))
+                    {
+                        var setAppHttpResponse = adminClient.PostAsync(
+                            StartupSupportingMigrations.PathApiSetAppConfigAndInitState,
+                            new ByteArrayContent(webAppConfigZipArchive)).Result;
+                    }
+                }
+
+                foreach (var eventsAndExpectedResponsesBatch in eventsAndExpectedResponsesBatches)
+                {
+                    using (var server = testSetup.BuildServer())
+                    {
+                        using (var adminClient = createClientWithAuthorizationHeader(server))
+                        {
+                            var setAppHttpResponse = adminClient.PostAsync(
+                                StartupSupportingMigrations.PathApiSetAppConfigAndContinueState,
+                                new ByteArrayContent(webAppConfigZipArchive)).Result;
+
+                            Assert.IsTrue(setAppHttpResponse.IsSuccessStatusCode, "set-app response IsSuccessStatusCode");
+                        }
+
+                        foreach (var (serializedEvent, expectedResponse) in eventsAndExpectedResponsesBatch)
+                        {
+                            using (var client = testSetup.BuildPublicAppHttpClient())
+                            {
+                                var httpResponse =
+                                    client.PostAsync("", new StringContent(serializedEvent, System.Text.Encoding.UTF8)).Result;
+
+                                var httpResponseContent = httpResponse.Content.ReadAsStringAsync().Result;
+
+                                Assert.AreEqual(expectedResponse, httpResponseContent, false, "server response matches " + expectedResponse);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
+
+        [TestMethod]
+        public void Web_host_supporting_migrations_supports_migrate_elm_state()
+        {
+            const string rootPassword = "Root-Password_1234567";
+
+            var webAppConfigZipArchive = ZipArchive.ZipArchiveFromEntries(
+                TestElmWebAppHttpServer.StringBuilderWebApp.AsFiles());
+
+            var migrateElmAppZipArchive = ZipArchive.ZipArchiveFromEntries(
+                TestSetup.GetElmAppFromExampleName("migrate-string-append-length"));
+
+            Func<IWebHostBuilder, IWebHostBuilder> webHostBuilderMap =
+                builder => builder.WithSettingAdminRootPassword(rootPassword);
+
+            HttpClient createClientWithAuthorizationHeader(Microsoft.AspNetCore.TestHost.TestServer server)
+            {
+                var adminClient = server.CreateClient();
+
+                adminClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(
+                    "Basic",
+                    Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(
+                        WebHost.Configuration.BasicAuthenticationForAdminRoot(rootPassword))));
+
+                return adminClient;
+            }
+
+            using (var testSetup = WebHostSupportingMigrationsTestSetup.Setup(webHostBuilderMap))
+            {
+                using (var server = testSetup.BuildServer())
+                {
+                    using (var adminClient = createClientWithAuthorizationHeader(server))
+                    {
+                        var setAppConfigResponse = adminClient.PostAsync(
+                            StartupSupportingMigrations.PathApiSetAppConfigAndInitState,
+                            new ByteArrayContent(webAppConfigZipArchive)).Result;
+
+                        Assert.IsTrue(setAppConfigResponse.IsSuccessStatusCode, "set-app response IsSuccessStatusCode");
+                    }
+
+                    using (var client = testSetup.BuildPublicAppHttpClient())
+                    {
+                        var httpResponse =
+                            client.PostAsync("", new StringContent("a", System.Text.Encoding.UTF8)).Result;
+
+                        var httpResponseContent = httpResponse.Content.ReadAsStringAsync().Result;
+
+                        Assert.AreEqual("a", httpResponseContent, false, "Server response content.");
+                    }
+
+                    using (var client = testSetup.BuildPublicAppHttpClient())
+                    {
+                        var httpResponse =
+                            client.PostAsync("", new StringContent("b", System.Text.Encoding.UTF8)).Result;
+
+                        var httpResponseContent = httpResponse.Content.ReadAsStringAsync().Result;
+
+                        Assert.AreEqual("ab", httpResponseContent, false, "Server response content.");
+                    }
+
+                    using (var adminClient = createClientWithAuthorizationHeader(server))
+                    {
+                        var migrateHttpResponse = adminClient.PostAsync(
+                            StartupSupportingMigrations.PathApiMigrateElmState,
+                            new ByteArrayContent(migrateElmAppZipArchive)).Result;
+
+                        Assert.IsTrue(migrateHttpResponse.IsSuccessStatusCode, "migrate-elm-state response IsSuccessStatusCode");
+                    }
+
+                    using (var client = testSetup.BuildPublicAppHttpClient())
+                    {
+                        var httpResponse =
+                            client.PostAsync("", new StringContent("c", System.Text.Encoding.UTF8)).Result;
+
+                        var httpResponseContent = httpResponse.Content.ReadAsStringAsync().Result;
+
+                        Assert.AreEqual("ab2c", httpResponseContent, false, "Server response content.");
+                    }
+                }
+            }
+        }
+
+        class FileStoreFromDelegates : IFileStore
+        {
+            readonly Action<IImmutableList<string>, byte[]> setFileContent;
+
+            readonly Action<IImmutableList<string>, byte[]> appendFileContent;
+
+            readonly Action<IImmutableList<string>> deleteFile;
+
+            readonly Func<IImmutableList<string>, byte[]> getFileContent;
+
+            readonly Func<IImmutableList<string>, IEnumerable<IImmutableList<string>>> listFilesInDirectory;
+
+            public FileStoreFromDelegates(
+                Action<IImmutableList<string>, byte[]> setFileContent,
+                Action<IImmutableList<string>, byte[]> appendFileContent,
+                 Action<IImmutableList<string>> deleteFile,
+                Func<IImmutableList<string>, byte[]> getFileContent,
+                Func<IImmutableList<string>, IEnumerable<IImmutableList<string>>> listFilesInDirectory)
+            {
+                this.setFileContent = setFileContent;
+                this.appendFileContent = appendFileContent;
+                this.deleteFile = deleteFile;
+                this.getFileContent = getFileContent;
+                this.listFilesInDirectory = listFilesInDirectory;
+            }
+
+            public void AppendFileContent(IImmutableList<string> path, byte[] fileContent) =>
+                appendFileContent(path, fileContent);
+
+            public void DeleteFile(IImmutableList<string> path) =>
+                deleteFile(path);
+
+            public byte[] GetFileContent(IImmutableList<string> path) =>
+                getFileContent(path);
+
+            public IEnumerable<IImmutableList<string>> ListFilesInDirectory(IImmutableList<string> directoryPath) =>
+                listFilesInDirectory(directoryPath);
+
+            public void SetFileContent(IImmutableList<string> path, byte[] fileContent) =>
+                setFileContent(path, fileContent);
+        }
+
+        class Web_host_propagates_HTTP_headers_Response_Entry
+        {
+            public string name = null;
+
+            public string[] values = null;
+        }
+
+        static HttpResponseMessage HttpGetAtRoot(
+            Microsoft.AspNetCore.TestHost.TestServer server)
+        {
+            using (var client = server.CreateClient())
+            {
+                return client.GetAsync("").Result;
+            }
+        }
+
+        static HttpResponseMessage HttpPostStringContentAtRoot(
+            Microsoft.AspNetCore.TestHost.TestServer server, string requestContent)
+        {
+            using (var client = server.CreateClient())
+            {
+                return
+                    client.PostAsync("", new StringContent(requestContent, System.Text.Encoding.UTF8)).Result;
+            }
+        }
+
+        static System.Threading.Tasks.Task<HttpResponseMessage> HttpSetPersistentProcessState(
+            HttpClient client,
+            string state) =>
+            client.PostAsync(
+                Kalmit.PersistentProcess.WebHost.Configuration.AdminPath +
+                Kalmit.PersistentProcess.WebHost.Configuration.ApiPersistentProcessStatePath,
+                new StringContent(state, System.Text.Encoding.UTF8));
+    }
 }
\ No newline at end of file