testing-best-practices

Test layering policy

Unit tests

Purpose: verify individual functions and invariants in isolation.

• Data-driven: parameterized tables covering happy path, boundary, error, and edge cases.
• Property-based: fuzz invariants that must hold across all inputs (e.g., idempotency, sort stability, roundtrip serialization).
• Derive cases from the module's public API surface: input types/constraints, output shape, error modes, invariants.

Integration / contract tests

Purpose: verify interactions between components and external services.

• API envelope: request/response shape, status codes, content types, pagination.
• Error contract: error codes, error shapes, rate limiting, retries.
• Auth and scoping: token validation, role-based access, tenant isolation.
• Eventual consistency: verify convergence within bounded time; poll rather than sleep.
• Reuse auth state across tests where possible; avoid redundant login flows.