String Inspection Guards

[feO2x]

Closes #153

Also upgrades xunit to v3, introduces Microsoft.Testing.Platform v2 and enabled code coverage reporting in GitHub Actions.

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
Light.GuardClauses	87%	84%	2336	✔
Light.GuardClauses.InternalRoslynAnalyzers	96%	86%	52	✔
Light.GuardClauses.InternalRoslynAnalyzers.CodeFixes	95%	100%	8	✔
Light.GuardClauses.SourceCodeTransformation	92%	83%	663	✔
Summary	89% (4186 / 4715)	84% (2316 / 2757)	3059	✔

[Copilot]

Pull request overview

Adds a new family of allocation-free string inspection predicates and fluent throwing guards (digits, letters-or-digits, casing, Base64, hex, and whitespace) across string, span, and memory receiver shapes, aligned with the library’s existing assertion patterns and source-export distribution model. The PR also updates the test/tooling stack to xUnit v3 on Microsoft Testing Platform and enables CI code coverage reporting.

Changes:

• Introduces string-inspection predicates (ContainsOnlyDigits, ContainsOnlyLettersOrDigits, IsUpperCase, IsLowerCase, IsBase64, IsHexadecimal) and guards (Must* variants plus MustNotContainWhiteSpace) for all required receiver shapes.
• Aligns MustBeAscii character-sequence overloads to throw StringException for invalid non-null string content (keeping scalar/byte overload behavior unchanged).
• Updates tests, source-export whitelist plumbing, benchmarks, docs, and GitHub Actions to support xUnit v3 + Microsoft Testing Platform with coverage artifacts and PR coverage comments.

Reviewed changes

Copilot reviewed 36 out of 37 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tools/source-export/Light.GuardClauses.SourceCodeTransformation/SourceFileMerger.cs	Ensures Net10 single-file exports include required framework usings for new Base64 APIs.
tools/source-export/Light.GuardClauses.SourceCodeTransformation/settings.json	Adds new string-inspection assertion families to the source-export whitelist settings.
tools/source-export/Light.GuardClauses.SourceCodeTransformation/AssertionWhitelist.cs	Extends whitelist model with entries for the new predicates/guards.
src/Light.GuardClauses/ExceptionFactory/Throw.InvalidStringContent.cs	Adds a centralized helper for throwing StringException for invalid string content.
src/Light.GuardClauses/Check.MustNotContainWhiteSpace.cs	Adds throwing-only whitespace rejection guard across all receiver shapes.
src/Light.GuardClauses/Check.MustContainOnlyLettersOrDigits.cs	Adds guard requiring Unicode letter-or-digit content across all receiver shapes.
src/Light.GuardClauses/Check.MustContainOnlyDigits.cs	Adds guard requiring Unicode digit content across all receiver shapes.
src/Light.GuardClauses/Check.MustBeUpperCase.cs	Adds guard requiring absence of Unicode lowercase characters across all receiver shapes.
src/Light.GuardClauses/Check.MustBeLowerCase.cs	Adds guard requiring absence of Unicode uppercase characters across all receiver shapes.
src/Light.GuardClauses/Check.MustBeHexadecimal.cs	Adds guard requiring ASCII hex content across all receiver shapes.
src/Light.GuardClauses/Check.MustBeBase64.cs	Adds guard requiring structurally valid standard Base64 across all receiver shapes.
src/Light.GuardClauses/Check.MustBeAscii.cs	Updates character-sequence MustBeAscii to throw StringException for invalid non-null content and refreshes XML docs.
src/Light.GuardClauses/Check.IsUpperCase.cs	Adds casing predicate (no lowercase chars) across all receiver shapes.
src/Light.GuardClauses/Check.IsLowerCase.cs	Adds casing predicate (no uppercase chars) across all receiver shapes.
src/Light.GuardClauses/Check.IsHexadecimal.cs	Adds hex predicate with Net10 fast-path (char.IsAsciiHexDigit) and portable fallback.
src/Light.GuardClauses/Check.IsBase64.cs	Adds Base64 predicate using Net10 Base64.IsValid and a portable validator fallback.
src/Light.GuardClauses/Check.ContainsOnlyLettersOrDigits.cs	Adds Unicode alphanumeric predicate across all receiver shapes.
src/Light.GuardClauses/Check.ContainsOnlyDigits.cs	Adds Unicode digit predicate across all receiver shapes.
tests/Directory.Build.props	Migrates test projects to Microsoft Testing Platform runner and enables TRX + coverage extensions.
tests/Light.GuardClauses.Tests/Test.cs	Updates test helper imports for xUnit v3 usage.
tests/Light.GuardClauses.Tests/StringAssertions/StringInspectionPredicateTests.cs	Adds conformance tests for predicate semantics + Base64 portability differential tests.
tests/Light.GuardClauses.Tests/StringAssertions/StringInspectionGuardTests.cs	Adds conformance tests for guard return-shape, null/invalid behavior, and custom factories.
tests/Light.GuardClauses.Tests/StringAssertions/OrdinalIgnoreWhiteSpaceComparerTests.cs	Updates output helper null-guard usage for new CallerArgumentExpression behavior.
tests/Light.GuardClauses.Tests/StringAssertions/OrdinalIgnoreCaseIgnoreWhiteSpaceComparerTests.cs	Updates output helper null-guard usage for new CallerArgumentExpression behavior.
tests/Light.GuardClauses.Tests/StringAssertions/AsciiTests.cs	Updates expectations for MustBeAscii string/span/memory exception behavior (StringException).
tests/Light.GuardClauses.Tests/DefaultVariablesData.cs	Updates custom data attribute for xUnit v3 discovery/data-row model (currently contains a compile error).
tests/Light.GuardClauses.SourceCodeTransformation.Tests/SourceFileMergerWhitelistTests.cs	Adds whitelist reachability/trimming tests for new string-inspection families and portable Base64 validator.
tests/Light.GuardClauses.SourceCodeTransformation.Tests/SourceFileMergerFrameworkTests.cs	Extends framework-conditional export tests to validate Net10 vs NetStandard Base64/hex compilation output.
tests/Light.GuardClauses.SourceCodeTransformation.Tests/ParseCSharpFilesWithRoslynTests.cs	Updates Roslyn parse calls to use the test cancellation token.
benchmarks/Light.GuardClauses.Performance/StringAssertions/StringInspectionBenchmark.cs	Adds microbenchmarks for new predicates/guards (digits, alphanumeric, Base64, whitespace).
docs/contributing-and-building.md	Updates local build/test instructions for Microsoft Testing Platform and coverage flags.
docs/assertion-overview.md	Documents the new string-inspection predicates/guards and their semantics.
Directory.Packages.props	Updates central package versions (BenchmarkDotNet/FluentAssertions) and switches to MTP + xUnit v3 packages.
global.json	Declares Microsoft Testing Platform as the test runner in repo configuration.
ai-plans/0153-string-inspection-guards.md	Adds the implementation plan/acceptance-criteria checklist for issue #153.
.github/workflows/build-and-test.yml	Updates CI triggers, runs tests with coverage, produces coverage artifacts, and posts a sticky PR coverage comment.

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