What problem does it solve? Choosing what to verify at the unit level versus the integration level is a common source of test suite bloat and gaps: logic branches leak into slow integration tests, or connection mismatches (SQL dialects, serialization, transaction boundaries) go untested. This Skill defines clear coverage criteria and execution procedures for both levels inside a single service. ## Core Features & Use Cases - Unit Test Guidance: Enumerate public behaviors, assign black-box techniques (equivalence partitioning, boundary values, decision tables), drive cases via TDD Red-Green cycles, and confirm completion with C1 branch coverage and MC-DC for safety-critical conditions. - Integration Test Guidance: Enumerate connection paths as a boundary-by-operation table, assign one representative success and failure case per boundary, and verify against real engines (e.g., Testcontainers) instead of in-memory substitutes. - Use Case: When building a repository layer over a real database, use the integration procedure to fix the exact number of tests needed (boundaries x representative cases) and detect shared-state pollution by running tests with shuffled ordering. ## Quick Start Ask the AI to apply the levels skill to design unit and integration tests for a specific module, listing its public behaviors and external dependency boundaries first.