feat: add comprehensive kitchen sink migration tests and improve code fixers

[thomhurst]

Summary

• Add comprehensive kitchen sink tests for NUnit, MSTest, and XUnit migrations covering setup/teardown hooks, various test attributes, assertion methods, collection assertions, and skip/ignore functionality
• Fix NUnit migration code fixer to handle Does.Contain(), Contains.Item(), and convert Description attribute to [Property("Description", "...")]
• All 864 migration tests pass (520 NUnit + 144 MSTest + 208 XUnit)

Test plan

• Run NUnit migration tests: dotnet test -- --treenode-filter "/*/*/NUnitMigrationAnalyzerTests/*" - 520 tests pass
• Run MSTest migration tests: dotnet test -- --treenode-filter "/*/*/MSTestMigrationAnalyzerTests/*" - 144 tests pass
• Run XUnit migration tests: dotnet test -- --treenode-filter "/*/*/XUnitMigrationAnalyzerTests/*" - 208 tests pass

🤖 Generated with Claude Code

[thomhurst]

Summary

Adds comprehensive migration test coverage (864 tests) and fixes critical bugs in code fixers for NUnit/MSTest/XUnit migration: stale node references in multi-class files, sibling attribute preservation, and NUnit assertion/attribute handling improvements.

Critical Issues

None found ✅

Suggestions

Code Quality Observations (Non-blocking)

1. BaseMigrationCodeFixProvider.cs:142-171 - The CleanupClassMemberLeadingTrivia fix properly addresses the Roslyn stale node reference bug by using a while loop with re-querying instead of iterating over a pre-collected list. This is the correct approach for working with immutable syntax trees.

2. BaseMigrationCodeFixProvider.cs:264-267 - The AttributeRewriter fix correctly prevents early return when converting hook attributes, preserving sibling attributes. This addresses the bug where [SetUp, Category("Unit")] would lose the Category attribute.

3. NUnitMigrationCodeFixProvider.cs:2077-2096 - Lifecycle method visibility fix properly handles removing existing access modifiers before adding public. The trivia handling looks correct.

4. Test Coverage - The kitchen sink tests provide excellent coverage:

   • 520 NUnit tests
   • 144 MSTest tests
   • 208 XUnit tests
   • Tests explicitly cover the bugs being fixed (sibling attributes, multiple classes)

TUnit Rules Compliance

• No dual-mode changes (not touching source-gen or reflection paths)
• No snapshot updates needed (not changing generator output or public APIs)
• No VSTest dependencies
• No blocking on async operations
• No hot path performance concerns
• No AOT compatibility issues

Verdict

✅ APPROVE - No critical issues. The changes properly fix Roslyn syntax tree mutation bugs and add comprehensive test coverage. All 864 tests pass as documented.