NUnit Migration: `using NUnit.Framework;` statements not removed

[thomhurst]

Description

When running the TUnit NUnit migration code fixer using dotnet format analyzers --severity info --diagnostics TUNU0001, the using NUnit.Framework; statements are not removed from the migrated files, even though TUnit usings are added.

Steps to Reproduce

1. Create a project with NUnit tests
2. Add TUnit packages
3. Run dotnet format analyzers --severity info --diagnostics TUNU0001
4. Build the project

Expected Behavior

The using NUnit.Framework; statements should be removed after migration since NUnit is no longer used.

Actual Behavior

The NUnit using statements remain, causing build errors when NUnit packages are removed:

error CS0246: The type or namespace name 'NUnit' could not be found

Example

Before migration:

using NUnit.Framework;

[TestFixture]
public class MyTests
{
    [Test]
    public void MyTest()
    {
        Assert.IsNotNull(someValue);
    }
}

After migration (current):

using System.Threading.Tasks;
using TUnit.Core;
using TUnit.Assertions;
using static TUnit.Assertions.Assert;
using TUnit.Assertions.Extensions;
// ... license header ...

using NUnit.Framework;  // <-- Still present

public class MyTests
{
    [Test]
    public async Task MyTest()
    {
        await Assert.That(someValue).IsNotNull();
    }
}

Expected after migration:

using System.Threading.Tasks;
using TUnit.Core;
using TUnit.Assertions;
using static TUnit.Assertions.Assert;
using TUnit.Assertions.Extensions;
// ... license header ...

// No NUnit using statement

public class MyTests
{
    [Test]
    public async Task MyTest()
    {
        await Assert.That(someValue).IsNotNull();
    }
}

Environment

• TUnit version: 1.9.91
• .NET version: .NET 8.0
• OS: Windows