fix: detect namespace-scoped TUnit.AspNetCore usings when applying co…

…de fix

Also guards against ignoring pre-existing top-level usings and adds tests
for both cases (top-level + namespace-scoped) so BatchFixer can't emit
duplicate directives.

TUnit.AspNetCore.Analyzers.CodeFixers/UseTestWebApplicationFactoryCodeFixProvider.cs

@@ -91,7 +91,8 @@ private static async Task<Document> ReplaceBaseTypeAsync(
 
     private static CompilationUnitSyntax AddUsingIfMissing(CompilationUnitSyntax compilationUnit, string namespaceName)
     {
-        if (compilationUnit.Usings.Any(u => u.Name?.ToString() == namespaceName))
+        if (ContainsUsing(compilationUnit.Usings, namespaceName) ||
+            compilationUnit.Members.Any(m => ContainsUsingInNamespace(m, namespaceName)))
         {
             return compilationUnit;
         }
@@ -101,4 +102,27 @@ private static CompilationUnitSyntax AddUsingIfMissing(CompilationUnitSyntax com
 
         return compilationUnit.AddUsings(newUsing);
     }
+
+    private static bool ContainsUsingInNamespace(MemberDeclarationSyntax member, string namespaceName) => member switch
+    {
+        BaseNamespaceDeclarationSyntax ns =>
+            ContainsUsing(ns.Usings, namespaceName) ||
+            ns.Members.Any(m => ContainsUsingInNamespace(m, namespaceName)),
+        _ => false,
+    };
+
+    private static bool ContainsUsing(SyntaxList<UsingDirectiveSyntax> usings, string namespaceName)
+    {
+        foreach (var directive in usings)
+        {
+            if (directive.Alias is null &&
+                directive.StaticKeyword.IsKind(SyntaxKind.None) &&
+                directive.Name?.ToString() == namespaceName)
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
 }

TUnit.AspNetCore.Analyzers.Tests/UseTestWebApplicationFactoryCodeFixProviderTests.cs

@@ -6,6 +6,72 @@ namespace TUnit.AspNetCore.Analyzers.Tests;
 
 public class UseTestWebApplicationFactoryCodeFixProviderTests
 {
+    [Test]
+    public async Task Does_Not_Duplicate_Existing_Using()
+    {
+        var source = $$"""
+            using TUnit.AspNetCore;
+            {{WebApplicationFactoryStubs.Source}}
+
+            public class MyFactory : {|#0:Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<Program>|}
+            {
+            }
+            """;
+
+        var fixedSource = $$"""
+            using TUnit.AspNetCore;
+            {{WebApplicationFactoryStubs.Source}}
+
+            public class MyFactory : TestWebApplicationFactory<Program>
+            {
+            }
+            """;
+
+        await Verifier.VerifyCodeFixAsync(
+            source,
+            fixedSource,
+            Verifier.Diagnostic(Rules.DirectWebApplicationFactoryInheritance)
+                .WithLocation(0)
+                .WithArguments("MyFactory"));
+    }
+
+    [Test]
+    public async Task Does_Not_Duplicate_Using_When_Imported_Inside_Namespace()
+    {
+        var source = $$"""
+            {{WebApplicationFactoryStubs.Source}}
+
+            namespace App
+            {
+                using TUnit.AspNetCore;
+
+                public class MyFactory : {|#0:Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<Program>|}
+                {
+                }
+            }
+            """;
+
+        var fixedSource = $$"""
+            {{WebApplicationFactoryStubs.Source}}
+
+            namespace App
+            {
+                using TUnit.AspNetCore;
+
+                public class MyFactory : TestWebApplicationFactory<Program>
+                {
+                }
+            }
+            """;
+
+        await Verifier.VerifyCodeFixAsync(
+            source,
+            fixedSource,
+            Verifier.Diagnostic(Rules.DirectWebApplicationFactoryInheritance)
+                .WithLocation(0)
+                .WithArguments("MyFactory"));
+    }
+
     [Test]
     public async Task Rewrites_Base_Type_To_TestWebApplicationFactory()
     {