Conciseness

The body is lean: short sections, no explanation of concepts Claude already knows, and every code block demonstrates a distinct test layer. Minor trimmable parts remain — the 'When to Use' section duplicates the frontmatter's use cases and the examples carry standard class scaffolding — matching anchor 4 (efficient with minor over-explanation) rather than the every-token-earns-its-place anchor 5.

Actionability

Concrete, executable code for each layer (unit, MockMvc, SpringBootTest, DataJpaTest), a JaCoCo Maven snippet, and CI commands — mostly copy-paste ready. It stops short of anchor 5 because Testcontainers guidance is bullet-only and the persistence example imports 'TestContainersConfig.class' which is never defined, leaving a gap in the common integration-test path.

Workflow Clarity

The TDD workflow is clearly sequenced ('Write tests first (they should fail)' → 'Implement minimal code to pass' → 'Refactor with tests green' → 'Enforce coverage') with checkpoints present as parenthetical conditions. It fits anchor 4 rather than 5 because verification is implicit (no explicit command to confirm red/green, e.g. 'run mvn test and confirm failure') and there is no error-recovery guidance.

Progressive Disclosure

A single-file skill with well-organized, clearly headed sections covering the full testing stack — good structure with content mostly appropriately placed. It does not qualify for the under-50-line simple-skill exception (the body is ~150 lines), and bulkable material like the JaCoCo plugin configuration or Testcontainers setup could live in one-level-deep reference files, keeping it at anchor 4.

Specificity

Names the domain ('Test-driven development for Spring Boot') and an explicit tool stack ('JUnit 5, Mockito, MockMvc, Testcontainers, and JaCoCo'), but the only action stated is 'test-driven development' itself — the enumerated items are tools, not actions. This matches anchor 3 (domain plus 1-2 concrete actions, not comprehensive) rather than anchor 4, which requires several specific action verbs.

Completeness

Both parts are present: a clear 'what' ('Test-driven development for Spring Boot using JUnit 5, Mockito, MockMvc, Testcontainers, and JaCoCo') and an explicit 'Use when adding features, fixing bugs, or refactoring' trigger clause with three concrete triggers. It does not reach anchor 5 because the trigger list is thinner and less varied than the comprehensive good example (no synonyms or additional trigger phrases).

Trigger Term Quality

'Use when adding features, fixing bugs, or refactoring' plus tool names (Spring Boot, JUnit 5, Testcontainers) gives good natural keyword coverage — phrases users would actually say. It falls short of anchor 5 because common variations like 'writing tests', 'unit tests', 'integration tests', or 'test coverage' are missing.

Distinctiveness Conflict Risk

The what-clause carves a clear niche (Spring Boot testing with a specific stack), but the when-clause ('adding features, fixing bugs, or refactoring') is broad enough to overlap with general coding or refactoring skills. This is 'mostly distinct; minor overlap risk with closely related skills' rather than the minimal-conflict anchor 5.