Fixes and additional coverage

Modules/OpenApi/Handler/OpenApiConcern.cs

@@ -39,7 +39,7 @@ public OpenApiConcern(IHandler content, ApiDiscoveryRegistry discovery, bool ena
 
     #region Functionality
 
-    public ValueTask PrepareAsync() => new();
+    public ValueTask PrepareAsync() => Content.PrepareAsync();
 
     public async ValueTask<IResponse?> HandleAsync(IRequest request)
     {

Testing/Acceptance/Engine/MainHandlerTests.cs

@@ -0,0 +1,63 @@
+using GenHTTP.Api.Content;
+using GenHTTP.Api.Protocol;
+using GenHTTP.Modules.Layouting;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+using StringContent = GenHTTP.Modules.IO.Strings.StringContent;
+
+namespace GenHTTP.Testing.Acceptance.Engine;
+
+[TestClass]
+public class MainHandlerTests
+{
+
+    #region Supporting data structures
+
+    public class PreparationHandler : IHandler
+    {
+        private bool _Prepared;
+
+        public ValueTask PrepareAsync()
+        {
+            _Prepared = true;
+            return new();
+        }
+
+        public ValueTask<IResponse?> HandleAsync(IRequest request)
+        {
+            var response = request.Respond()
+                                  .Content(new StringContent(_Prepared ? "prepared" : "not prepared"))
+                                  .Build();
+
+            return new(response);
+        }
+
+    }
+
+    #endregion
+
+    [TestMethod]
+    [MultiEngineTest]
+    public async Task TestHandlerPreparation(TestEngine engine)
+    {
+        await using var host = await TestHost.RunAsync(new PreparationHandler(), engine: engine);
+
+        using var response = await host.GetResponseAsync();
+
+        Assert.AreEqual("prepared", await response.GetContentAsync());
+    }
+
+    [TestMethod]
+    [MultiEngineTest]
+    public async Task TestLayoutHandlerPreparation(TestEngine engine)
+    {
+        var app = Layout.Create().Add("sub", new PreparationHandler());
+
+        await using var host = await TestHost.RunAsync(app, engine: engine);
+
+        using var response = await host.GetResponseAsync("/sub/");
+
+        Assert.AreEqual("prepared", await response.GetContentAsync());
+    }
+
+}

Testing/Acceptance/Modules/ApiBrowsing/HandlerTests.cs

@@ -4,7 +4,7 @@
 using GenHTTP.Modules.Layouting;
 using GenHTTP.Modules.Layouting.Provider;
 using GenHTTP.Modules.OpenApi;
-
+using GenHTTP.Testing.Acceptance.Utilities;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 
 namespace GenHTTP.Testing.Acceptance.Modules.ApiBrowsing;
@@ -71,6 +71,12 @@ public async Task TestCustomMeta(TestEngine engine)
         AssertX.Contains("My API", content);
     }
 
+    [TestMethod]
+    public void TestConcernChaining()
+    {
+        Chain.Works(ApiBrowser.Redoc());
+    }
+
     private static LayoutBuilder GetApi()
     {
         return Layout.Create()