Conciseness

The body is lean and directive throughout — "No `sleep`: wait for the condition (`waitFor`, an assertion that polls)", "never retry it into green" — with no explanation of concepts Claude already knows and every token earning its place, matching anchor 5.

Actionability

As an instruction-only skill, the guidance is concrete and executable: specific edge cases to cover ("empty results, the boundaries, invalid input, a failing network or dependency, the same action twice"), a concrete API ("`waitFor`, an assertion that polls"), and hard limits ("One suite per session, at most three screenshots"), satisfying anchor 5 under the instruction-skill scoring note.

Workflow Clarity

The Test-first section gives a clear three-step sequence with explicit validation checkpoints ("watch it fail, for the reason you expect"; "Clean up with the test green"), but there is no explicit error-recovery loop and the remaining sections are checklists rather than sequenced workflow, fitting anchor 4 better than 5.

Progressive Disclosure

The skill is under 50 lines with no need for external references (no bundle files exist), and its five well-organized sections (Test first, What to cover, Mocks, Flaky tests, E2E) make navigation trivial, which scores 5 under the simple-skill guideline.

Specificity

The description lists several concrete facets — "test first, what to cover, what to mock, and the anti-patterns that let tests pass without proving anything" — but omits the E2E-session guidance present in the body, a minor coverage gap that keeps it below the comprehensive anchor 5.

Completeness

It explicitly answers both questions: the "what" ("How to test a change: test first, what to cover, what to mock, and the anti-patterns...") and a concrete "when" ("Use when writing or planning tests, mocking a dependency, fixing a flaky test, or checking coverage"), matching anchor 5.

Trigger Term Quality

The "Use when" clause includes natural phrases users would say — "writing or planning tests, mocking a dependency, fixing a flaky test, or checking coverage" — but misses common variations like "unit tests", "TDD", or "test suite", matching the good-but-not-comprehensive anchor 4.

Distinctiveness Conflict Risk

The testing niche is mostly distinct with specific triggers ("fixing a flaky test", "checking coverage"), but the broad phrase "writing or planning tests" creates minor overlap risk with the e2e-testing and browser-testing skills the body itself references, fitting anchor 4 rather than the minimal-conflict anchor 5.