Code fixer converts [Platform] attribute to non-existent [ExcludeOn(OS.X)] attribute

[thomhurst]

Description

The NUnit migration code fixer (TUNU0001) converts NUnit's [Platform] attribute to [ExcludeOn(OS.X)], but neither the ExcludeOn attribute nor the OS enum exist in TUnit. This results in compilation errors.

Reproduction Steps

1. Create a file with NUnit Platform attributes:

using NUnit.Framework;

public class TestClass
{
    [Test]
    [Platform(Exclude = "Mono")]
    public void Test_ExcludeMono() { }

    [Test]
    [Platform(Exclude = "Net")]
    public void Test_ExcludeNet() { }

    [Test]
    [Platform(Exclude = "Net,NetCore")]
    public void Test_ExcludeNetAndNetCore() { }
}

2. Run the code fixer: dotnet format analyzers --severity info --diagnostics TUNU0001

3. The code is converted to:

using System.Threading.Tasks;

public class TestClass
{
    [Test]
    [ExcludeOn(OS.Mono)]
    public async Task Test_ExcludeMono() { }

    [Test]
    [ExcludeOn(OS.Net)]
    public async Task Test_ExcludeNet() { }

    [Test]
    [ExcludeOn(OS.Net | OS.NetCore)]
    public async Task Test_ExcludeNetAndNetCore() { }
}

4. Building produces errors:

error CS0246: The type or namespace name 'ExcludeOn' could not be found
error CS0103: The name 'OS' does not exist in the current context

Expected Behavior

The code fixer should either:

1. Convert Platform attributes to TUnit's equivalent skip mechanism (custom SkipAttribute)
2. Leave a TODO comment indicating manual migration is required
3. Not convert the attribute at all if no direct equivalent exists

Environment

• TUnit Version: 1.11.64
• .NET SDK: 10.0.100-preview.1.25103.12
• OS: Windows 11

Additional Context

TUnit's recommended approach for platform-specific test skipping is to create custom skip attributes by extending SkipAttribute. The code fixer is generating references to types that don't exist in TUnit.

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Note: Please add tests when fixing this issue to prevent regression.