add support for xunit SetAsserts Subset

src/FluentAssertions.Analyzers.Tests/Tips/XunitTests.cs

@@ -540,6 +540,20 @@ public void AssertStartsWith_TestAnalyzer(string assertion) =>
         public void AssertStartsWith_TestCodeFix(string oldAssertion, string newAssertion)
             => VerifyCSharpFix<AssertStartsWithCodeFix, AssertStartsWithAnalyzer>("string actual, string expected", oldAssertion, newAssertion);
 
+        [DataTestMethod]
+        [DataRow("Assert.Subset(expected, actual);")]
+        [Implemented]
+        public void AssertSubset_TestAnalyzer(string assertion) =>
+            VerifyCSharpDiagnostic<AssertSubsetAnalyzer>("ISet<string> actual, ISet<string> expected", assertion);
+
+        [DataTestMethod]
+        [DataRow(
+            /* oldAssertion: */ "Assert.Subset(expected, actual);",
+            /* newAssertion: */ "actual.Should().BeSubsetOf(expected);")]
+        [Implemented]
+        public void AssertSubset_TestCodeFix(string oldAssertion, string newAssertion)
+            => VerifyCSharpFix<AssertSubsetCodeFix, AssertSubsetAnalyzer>("ISet<string> actual, ISet<string> expected", oldAssertion, newAssertion);
+
         private void VerifyCSharpDiagnostic<TDiagnosticAnalyzer>(string methodArguments, string assertion) where TDiagnosticAnalyzer : Microsoft.CodeAnalysis.Diagnostics.DiagnosticAnalyzer, new()
         {
             var source = GenerateCode.XunitAssertion(methodArguments, assertion);

src/FluentAssertions.Analyzers/Constants.cs

@@ -136,6 +136,7 @@ public static class Xunit
                 public const string AssertEmpty = $"{DiagnosticProperties.IdPrefix}0714";
                 public const string AssertEndsWith = $"{DiagnosticProperties.IdPrefix}0715";
                 public const string AssertStartsWith = $"{DiagnosticProperties.IdPrefix}0716";
+                public const string AssertSubset = $"{DiagnosticProperties.IdPrefix}0717";
             }
         }
 

src/FluentAssertions.Analyzers/Tips/Xunit/AssertSubset.cs

@@ -0,0 +1,57 @@
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Composition;
+using FluentAssertions.Analyzers.Utilities;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace FluentAssertions.Analyzers.Xunit;
+
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public class AssertSubsetAnalyzer : XunitAnalyzer
+{
+    public const string DiagnosticId = Constants.Tips.Xunit.AssertSubset;
+    public const string Category = Constants.Tips.Category;
+
+    public const string Message = "Use .Should().BeSubset()";
+
+    protected override DiagnosticDescriptor Rule => new(DiagnosticId, Title, Message, Category, DiagnosticSeverity.Info, true);
+
+    protected override IEnumerable<FluentAssertionsCSharpSyntaxVisitor> Visitors => new FluentAssertionsCSharpSyntaxVisitor[]
+    {
+        new AssertSubsetSyntaxVisitor()
+    };
+
+    //public static void Subset(ISet expectedSubset, ISet? actual)
+    public class AssertSubsetSyntaxVisitor : FluentAssertionsCSharpSyntaxVisitor
+    {
+        public AssertSubsetSyntaxVisitor() : base(
+            MemberValidator.ArgumentsMatch("Subset",
+                ArgumentValidator.Exists(),
+                ArgumentValidator.IsTypeOrConstructedFromTypeOrImplementsType(SpecialType.System_Collections_IEnumerable))
+        )
+        {
+        }
+    }
+}
+
+[ExportCodeFixProvider(LanguageNames.CSharp, Name = nameof(AssertSubsetCodeFix)), Shared]
+public class AssertSubsetCodeFix : XunitCodeFixProvider
+{
+    public override ImmutableArray<string> FixableDiagnosticIds => ImmutableArray.Create(AssertSubsetAnalyzer.DiagnosticId);
+
+    protected override ExpressionSyntax GetNewExpression(
+        ExpressionSyntax expression,
+        FluentAssertionsDiagnosticProperties properties)
+    {
+        switch (properties.VisitorName)
+        {
+            case nameof(AssertSubsetAnalyzer.AssertSubsetSyntaxVisitor):
+                return RenameMethodAndReorderActualExpectedAndReplaceWithSubjectShould(expression, "Subset", "BeSubsetOf");
+            default:
+                throw new System.InvalidOperationException($"Invalid visitor name - {properties.VisitorName}");
+        }
+    }
+}