Improve test coverage: edge cases + fix bool/string switch key formatting

[Copilot]

Test coverage was missing several code paths in the generator, including one active bug where bool and string values used as [SwitchCase] keys produced invalid C# code.

Bug Fix

GeneratesMethodPatternSourceBuilder.cs — GenerateSwitchMethodSource used key.ToString() for all non-enum switch keys, which:

• Produced case True: / case False: for bool (not valid C# — needs true/false)
• Produced case hello: for string (missing quotes)

Added FormatKeyAsCSharpLiteral to handle these types correctly:

// Before: key.ToString()! for all non-enum types
// After:
return key switch
{
    bool b => b ? "true" : "false",
    // SyntaxFactory.Literal handles escaping and quoting (e.g. "hello" → "\"hello\"")
    string s => SyntaxFactory.Literal(s).Text,
    _ => key.ToString()!
};

New Tests

EdgeCaseSimplePatternTests.cs — covers previously untested branches in GeneratesMethodPatternSourceBuilder:

• Void return — if (!partialMethod.ReturnsVoid) skip-return branch
• Bool return — FormatValueAsCSharpLiteral System_Boolean case (emits true/false)
• Char return — FormatValueAsCSharpLiteral System_Char case (emits 'A')
• internal accessibility — AppendNamespaceAndTypeHeader Accessibility.Internal branch

BoolSwitchKeyTests.cs — end-to-end integration test for [SwitchCase(arg1: true/false)] verifying correct key formatting in generated code.

GeneratorDiagnosticsTests.cs additions:

• MSGH001 is emitted when [GeneratesMethod] targets a method that exists but is not partial
• Valid bool switch configuration produces no error diagnostics

Original prompt

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This section details on the original issue you should resolve

<issue_title>Improve test converage</issue_title>
<issue_description>Test coverage is not the best. Create test cases that test edge cases and improve test coverage.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Improve test converage #44

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[Copilot]

Pull request overview

Improves the GeneratesMethod source generator’s correctness and test coverage by fixing invalid switch case label formatting for non-enum keys (notably bool and string) and adding new tests to cover previously untested branches and diagnostics.

Changes:

• Fix: format bool and string [SwitchCase] keys as valid C# literals when generating switch statements.
• Add: new edge-case tests for void/bool/char return literals and internal accessibility generation.
• Add: diagnostic tests for MSGH001 (target method exists but isn’t partial) and for valid bool switch configurations producing no errors.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
MattSourceGenHelpers.Tests/EdgeCaseSimplePatternTests.cs	Adds runtime + generated-code assertions for void/bool/char returns and internal accessibility branch coverage.
MattSourceGenHelpers.Tests/BoolSwitchKeyTests.cs	Adds an integration test validating bool switch key generation produces case true/false.
MattSourceGenHelpers.Generators/GeneratesMethodPatternSourceBuilder.cs	Introduces FormatKeyAsCSharpLiteral and uses it for switch-case key emission.
MattSourceGenHelpers.GeneratorTests/GeneratorDiagnosticsTests.cs	Adds coverage for MSGH001 scenario and validates no error diagnostics for valid bool switch usage.

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[Copilot]

FormatKeyAsCSharpLiteral fixes bool/string, but char switch keys will still generate invalid C# (e.g., [SwitchCase(arg1: 'A')] will end up as case A: because the fallback uses key.ToString()). Consider handling char (and potentially other primitive literal types) similarly to FormatValueAsCSharpLiteral, e.g., use SyntaxFactory.Literal(c).Text when key is char or when parameterType.SpecialType == System_Char.

Suggested change

	return key switch
	{
	bool b => b ? "true" : "false",
	// SyntaxFactory.Literal handles escaping and quoting (e.g. "hello" → "\"hello\"")
	string s => SyntaxFactory.Literal(s).Text,
	// Handle char keys explicitly to produce valid C# char literals (e.g., 'A')
	if (parameterType?.SpecialType == SpecialType.System_Char)
	{
	if (key is char c)
	{
	return SyntaxFactory.Literal(c).Text;
	}
	var s = key.ToString() ?? string.Empty;
	if (s.Length == 1)
	{
	return SyntaxFactory.Literal(s[0]).Text;
	}
	// Fallback: treat as string literal; this should not normally be hit for valid char keys
	return SyntaxFactory.Literal(s).Text;
	}
	return key switch
	{
	bool b => b ? "true" : "false",
	// SyntaxFactory.Literal handles escaping and quoting (e.g. "hello" → "\"hello\"")
	string s => SyntaxFactory.Literal(s).Text,
	char c => SyntaxFactory.Literal(c).Text,

[Copilot]

The new string s => SyntaxFactory.Literal(s).Text branch in FormatKeyAsCSharpLiteral isn’t covered by a test (current new integration coverage only exercises the bool branch). Consider adding an end-to-end test similar to BoolSwitchKeyTests but with a string switch parameter (including a value that needs escaping) to prevent regressions in quoting/escaping.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 61.53846% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
....Generators/GeneratesMethodPatternSourceBuilder.cs	61.53%	3 Missing and 2 partials ⚠️

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