go-test-coverage

name	go-test-coverage
description	Analyzes Go test coverage and suggests improvements

Go Test Coverage Skill

Coverage numbers are a floor, not a ceiling. A test that executes code but asserts nothing is noise. Semantic coverage is what matters: do your tests catch real bugs? Mutation testing (Gremlins) validates this by introducing small bugs — if your tests pass, they are too weak.

1. [ ] Tests assert specific return values — not just `err == nil` 2. [ ] Table-driven tests for multiple scenarios using `t.Run` 3. [ ] Error branches tested explicitly 4. [ ] Edge cases: empty/nil input, zero values, boundary conditions 5. [ ] Tests deterministic — no `time.Now()`, no global state, no random without seed 6. [ ] Mocks implement port interfaces, not concrete types 7. [ ] Integration tests use `//go:build integration` tag 8. [ ] Coverage ≥80% on `internal/domain` and `internal/app` 9. [ ] Test file naming: `foo_test.go` alongside `foo.go` 10. [ ] `make ci` passes with all tests

<mutation_testing> Run make mutation-test-dry for a fast check. For critical domain code, run make mutation-test:

1. [ ] `make mutation-test-dry` passes (mutants are testable) 2. [ ] Mutation score ≥80% (80%+ of mutants killed) 3. [ ] No "LIVED" mutants on critical code paths (tests should catch introduced bugs) 4. [ ] If mutation score is low, add specific assertions that would fail on the mutant BAD: `result, err := Add(2, 3); assert.NoError(t, err)` — mutation changes `+` to `-`, test still passes GOOD: `result, _ := Add(2, 3); assert.Equal(t, 5, result)` — mutation caught, assertion fails