TUXU0001 code fixer does not remove all 'using Xunit;' statements

[thomhurst]

Description

When running the TUXU0001 code fixer for xUnit migration, the code fixer adds TUnit usings but does not consistently remove the using Xunit; statements, leaving them in some files.

Steps to Reproduce

1. Create a test file with xUnit:

using System.Threading.Tasks;

namespace Moq.Tests.Async
{
    using System.Threading.Tasks;
    using Moq.Async;
    using Xunit;

    public class AwaitableFixture
    {
        [Fact]
        public void TryGetResultRecursive_is_recursive()
        {
            const int expectedResult = 42;
            var obj = Task.FromResult(Task.FromResult(expectedResult));
            var result = Awaitable.TryGetResultRecursive(obj);
            Assert.Equal(expectedResult, result);
        }
    }
}

2. Install TUnit package alongside xUnit
3. Run the code fixer: dotnet format analyzers --severity warn --diagnostics TUXU0001

Expected Behavior

The using Xunit; statement should be removed and replaced with appropriate TUnit usings:

using System.Threading.Tasks;

namespace Moq.Tests.Async
{
    using System.Threading.Tasks;
    using Moq.Async;
    // using Xunit; should be removed

    public class AwaitableFixture
    {
        [Test]
        public async Task TryGetResultRecursive_is_recursive()
        {
            // ...
        }
    }
}

Actual Behavior

The code fixer converts the test attributes and assertions but leaves the using Xunit; statement in place:

using System.Threading.Tasks;

namespace Moq.Tests.Async
{
    using System.Threading.Tasks;
    using Moq.Async;
    using Xunit;  // <-- Still present!

    public class AwaitableFixture
    {
        [Test]  // Converted
        public async Task TryGetResultRecursive_is_recursive()
        {
            // Converted assertions
        }
    }
}

This causes:

• CS0246: The type or namespace name 'Xunit' could not be found after removing xUnit package

Environment

• TUnit Version: 1.11.64
• .NET SDK: 10.0.102
• OS: Windows

Observation

This may be related to the using statement being inside a namespace block rather than at the file level.

Tests to Add

Please add tests for:

1. using Xunit; at file level
2. using Xunit; inside namespace block
3. Multiple using statements on same line
4. Using alias like using X = Xunit;

[claude]

This issue appears related to #4471, #4417, and #4381, which were closed earlier today. However, this report identifies a specific edge case: using statements inside namespace blocks rather than at file level.

The previous issues show examples with file-level using statements:

using Xunit;

public class MyTests { }

But this issue specifically demonstrates the problem with namespace-scoped using statements:

namespace Moq.Tests.Async
{
    using Xunit;  // <-- Inside namespace
    
    public class AwaitableFixture { }
}

This is likely a separate code path in the Roslyn syntax tree that the code fixer needs to handle. The suggested test cases in the issue description are excellent and should definitely be added.