add support for xunit StringAsserts Empty (#226)

* add support for xunit StringAsserts Empty

Author: Meir017

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

@@ -424,6 +424,19 @@ public void AssertStringDoesNotMatch_Regex_TestAnalyzer(string assertion) =>
         public void AssertStringDoesNotMatch_Regex_TestCodeFix(string oldAssertion, string newAssertion)
             => VerifyCSharpFix<AssertDoesNotMatchCodeFix, AssertDoesNotMatchAnalyzer>("string actual, Regex expectedRegex", oldAssertion, newAssertion);
 
+        [DataTestMethod]
+        [DataRow("Assert.Empty(actual);")]
+        [Implemented]
+        public void AssertEmpty_String_TestAnalyzer(string assertion) =>
+            VerifyCSharpDiagnostic<AssertEmptyAnalyzer>("string actual", assertion);
+
+        [DataTestMethod]
+        [DataRow(
+            /* oldAssertion: */ "Assert.Empty(actual);",
+            /* newAssertion: */ "actual.Should().BeEmpty();")]
+        [Implemented]
+        public void AssertEmpty_String_TestCodeFix(string oldAssertion, string newAssertion)
+            => VerifyCSharpFix<AssertEmptyCodeFix, AssertEmptyAnalyzer>("string actual", oldAssertion, newAssertion);
 
         private void VerifyCSharpDiagnostic<TDiagnosticAnalyzer>(string methodArguments, string assertion) where TDiagnosticAnalyzer : Microsoft.CodeAnalysis.Diagnostics.DiagnosticAnalyzer, new()
         {

src/FluentAssertions.Analyzers/Constants.cs

@@ -133,6 +133,7 @@ public static class Xunit
                 public const string AssertDoesNotContain = $"{DiagnosticProperties.IdPrefix}0711";
                 public const string AssertMatches = $"{DiagnosticProperties.IdPrefix}0712";
                 public const string AssertDoesNotMatch = $"{DiagnosticProperties.IdPrefix}0713";
+                public const string AssertEmpty = $"{DiagnosticProperties.IdPrefix}0714";
             }
         }
 

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

@@ -0,0 +1,56 @@
+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 AssertEmptyAnalyzer : XunitAnalyzer
+{
+    public const string DiagnosticId = Constants.Tips.Xunit.AssertEmpty;
+    public const string Category = Constants.Tips.Category;
+
+    public const string Message = "Use .Should().NotMatchRegex()";
+
+    protected override DiagnosticDescriptor Rule => new(DiagnosticId, Title, Message, Category, DiagnosticSeverity.Info, true);
+
+    protected override IEnumerable<FluentAssertionsCSharpSyntaxVisitor> Visitors => new FluentAssertionsCSharpSyntaxVisitor[]
+    {
+        new AssertEmptyStringSyntaxVisitor()
+    };
+
+    //public static void Empty(string value)
+    public class AssertEmptyStringSyntaxVisitor : FluentAssertionsCSharpSyntaxVisitor
+    {
+        public AssertEmptyStringSyntaxVisitor() : base(
+            MemberValidator.ArgumentsMatch("Empty",
+                ArgumentValidator.IsType(TypeSelector.GetStringType))
+        )
+        {
+        }
+    }
+}
+
+[ExportCodeFixProvider(LanguageNames.CSharp, Name = nameof(AssertEmptyCodeFix)), Shared]
+public class AssertEmptyCodeFix : XunitCodeFixProvider
+{
+    public override ImmutableArray<string> FixableDiagnosticIds => ImmutableArray.Create(AssertEmptyAnalyzer.DiagnosticId);
+
+    protected override ExpressionSyntax GetNewExpression(
+        ExpressionSyntax expression,
+        FluentAssertionsDiagnosticProperties properties)
+    {
+        switch (properties.VisitorName)
+        {
+            case nameof(AssertEmptyAnalyzer.AssertEmptyStringSyntaxVisitor):
+                return RenameMethodAndReplaceWithSubjectShould(expression, "Empty", "BeEmpty");
+            default:
+                throw new System.InvalidOperationException($"Invalid visitor name - {properties.VisitorName}");
+        }
+    }
+}