Universal principles for writing good tests. These apply regardless of framework, language, or repo — discover and follow your repo's specific testing tools, commands, and conventions from its project configuration, contributor guides, existing test files, CI/CD config, and any repo-level AI skills or rules.
Tests verify behavior through public interfaces, not implementation details. Code can change entirely; tests shouldn't break unless behavior changed.
Good tests exercise real code paths through public APIs. They describe what the system does, not how. A good test reads like a specification — "user can checkout with valid cart" tells you exactly what capability exists. These tests survive refactors because they don't care about internal structure.
Universal test-driven development methodology and test design craft. Background knowledge for writing behavior-focused tests, mocking strategy, vertical slicing, and tracer bullet execution. Auto-loaded when writing tests during implementation, review feedback, or standalone test authoring. Triggers: writing tests, test design, mocking strategy, test quality, behavior testing, integration testing, test-first, red-green-refactor. Source: inkeep/team-skills.