What problem does it solve?
Raising test coverage often produces vacuous assertions that pass even when the code under test is deleted, giving a false sense of safety. This Skill closes coverage gaps in the microsoft/microsoft-ui-reactor repo with tests whose assertions genuinely fail if the targeted code path is removed, no-op'd, or returns a default value.
Core Features & Use Cases
- Coverage baselining and gap classification: Runs tools/coverage scripts, parses merged Cobertura XML for exact uncovered lines, and classifies each gap into the right tier — headless xUnit unit tests, WinUI selftest fixtures, or E2E input tests.
- Non-vacuous oracle patterns: Enforces proven assertion styles such as throw-position/arity oracles, differential isolation, reflection DeclaringType checks, and corrupt-then-recompute, and mutation-checks key assertions by breaking product code and confirming the test fails.
- Repo-specific build and test discipline: Encodes the x64 platform flags, SkipSignaturesGen workaround, fixture registry registration rules, and the dotnet test switch trap (issue #1140) so runs actually execute instead of silently reporting zero tests.
- Use Case: A contributor asks to "add tests for the PathDataParser". The Skill baselines coverage, identifies the internal tokenizer entry point as a unit-testable seam, writes narrowly-scoped xUnit tests with differential oracles, mutation-verifies them, and reports the coverage delta.
Quick Start
Ask the assistant to improve test coverage for a specific area of the microsoft-ui-reactor repo, for example by saying "raise coverage for the layout engine with non-vacuous tests".
