Add comprehensive test coverage for four CodeFix modules

[github-actions]

Summary

This PR significantly improves test coverage for four CodeFix modules that previously had minimal testing (1-2 test cases each). Added 23 new comprehensive test cases to provide thorough coverage of various scenarios and edge cases.

CodeFix Modules Enhanced

1. AddMissingFunKeyword (1 → 7 test cases, +6 new)

Original Coverage: Only tested basic x -> ... lambda syntax
Enhanced Coverage:

• Multiple parameters: x y z -> ...
• Nested expressions in List.map contexts
• Complex expression bodies with let bindings
• Tuple parameters: (a, b) -> ...
• Piping contexts with filtering/mapping

2. AddMissingRecKeyword (1 → 6 test cases, +5 new)

Original Coverage: Only tested simple mutual recursion
Enhanced Coverage:

• Pattern matching in recursive functions (isEven/isOdd)
• Complex expressions with Fibonacci-style recursion
• Type annotations on recursive function parameters
• Three-way mutual recursion scenarios
• Complex parameter handling with record updates

3. ChangeEqualsInFieldTypeToColon (2 → 8 test cases, +6 new)

Original Coverage: Basic single-line and multi-line record fields
Enhanced Coverage:

• Complex type annotations: list<string>
• Generic types: 'T
• Option types: int option
• Tuple types: int * int
• Function types: string -> int
• Nested records with proper indentation handling

4. ChangePrefixNegationToInfixSubtraction (1 → 7 test cases, +6 new)

Original Coverage: Only tested list slicing scenario
Enhanced Coverage:

• Arithmetic expressions: x + y -5
• Complex arithmetic: a * b + c -10 / 2
• Array indexing: arr.[index..lastIndex -1]
• Function call contexts: List.take (count -2)
• Nested expressions in match statements
• Variable name scenarios

Impact

• Total new test cases: 23
• Lines of test code added: 393
• Coverage improvement: Comprehensive coverage for four important CodeFix modules
• Edge cases covered: Complex expressions, type annotations, nested contexts, various syntax patterns

Test Quality

All new tests follow the existing patterns and conventions:

• Use meaningful test case names describing the specific scenario
• Test realistic F# code patterns that users would encounter
• Cover both simple and complex use cases
• Maintain proper error code expectations (10, 576, 3)
• Use appropriate cursor positioning ($0) for CodeFix triggering

Validation

✅ Build passes successfully with dotnet build -c Release
✅ All tests follow existing patterns and conventions
✅ No coverage files included in commit (verified)

This enhancement addresses the identified gaps from the Daily Test Coverage Improvement analysis and provides solid foundation for these CodeFix modules.

AI-generated content by Daily Test Coverage Improve may contain mistakes.