Increase Code Coverage

[feO2x]

Increases code coverage for the Light.GuardClauses project

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
Light.GuardClauses	95%	88%	2336	✔
Light.GuardClauses.InternalRoslynAnalyzers	96%	86%	52	✔
Light.GuardClauses.InternalRoslynAnalyzers.CodeFixes	95%	100%	8	✔
Light.GuardClauses.SourceCodeTransformation	92%	83%	663	✔
Summary	94% (4445 / 4715)	87% (2397 / 2757)	3059	✔

[Copilot]

Pull request overview

This PR increases test coverage across Light.GuardClauses by adding/expanding unit tests for guard clause overloads (including span/memory buffer shapes) and several framework extension helpers, and by documenting test-writing expectations.

Changes:

• Added new tests to cover additional success/failure paths and “factory not invoked on success” scenarios across string/numeric/buffer guard clauses.
• Added new tests for framework extension helpers (text/exception message formatting, enumerable counting, hash generation, string representations).
• Introduced test guidelines documentation and linked it from the root AGENTS.md; added solution items for easier discovery.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tests/Light.GuardClauses.Tests/StringAssertions/MustNotStartWithTests.cs	Adds span overload coverage and additional factory/success+failure path assertions.
tests/Light.GuardClauses.Tests/StringAssertions/MustBeEmailAddressTests.cs	Adjusts existing tests and adds buffer-overload success-path coverage.
tests/Light.GuardClauses.Tests/StringAssertions/AsciiTests.cs	Expands ASCII validation tests, including “factory not invoked” success-path checks.
tests/Light.GuardClauses.Tests/FrameworkExtensions/ToStringRepresentationTests.cs	Adds coverage for primitive/unquoted handling, nulls, and representation edge cases.
tests/Light.GuardClauses.Tests/FrameworkExtensions/TextExtensionsTests.cs	Adds coverage for exception message aggregation and whitespace-ignoring equality.
tests/Light.GuardClauses.Tests/FrameworkExtensions/MultiplyAddHashTests.cs	Adds coverage ensuring all supported CreateHashCode arities match the builder behavior.
tests/Light.GuardClauses.Tests/FrameworkExtensions/EnumerableCountTests.cs	Adds coverage for optimized counting strategies and enumeration behavior.
tests/Light.GuardClauses.Tests/ComparableAssertions/NumericCustomFactorySuccessTests.cs	Adds coverage that custom factories are not invoked on numeric success paths.
tests/AGENTS.md	Introduces explicit test-writing rules and how to run coverage.
Light.GuardClauses.slnx	Adds solution items to surface new build/test guidance files.
AGENTS.md	Links root guidance to the new test-specific guidance document.

Comments suppressed due to low confidence (1)

tests/Light.GuardClauses.Tests/StringAssertions/MustBeEmailAddressTests.cs:38

• This test is named InvalidEmailAddressArgumentName but it no longer asserts the exception's ParamName; it currently duplicates InvalidEmailAddress by only checking the message. Asserting ParamName here makes the intent explicit and prevents regressions in argument-name handling.

        act.Should().Throw<InvalidEmailAddressException>()
           .And.Message.Should().Contain(
                $"emailAddress must be a valid email address, but it actually is \"{emailAddress}\"."
            );
    }

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