API Testing

When to use

• Writing integration tests for REST or GraphQL endpoints (SuperTest, REST Assured, httpx)
• Setting up contract testing between consumer and provider services with Pact
• Validating API responses against an OpenAPI spec or JSON Schema
• Configuring WireMock or MSW to stub external dependencies in tests
• Auditing coverage of an existing API test suite against the HTTP scenario checklist
• Running Newman collections in CI pipelines
• Setting performance baselines for critical endpoints

Core principles

1. Test the contract, not the implementation — verify what the API returns, not how it produces it
2. Every status code is a scenario — 200 is one test; 400, 401, 403, 404, 429 are five more
3. Mock at the network boundary — WireMock/MSW intercept at the wire; never mock internal service methods
4. Tokens come from helpers, never fixtures — hardcoded tokens in test files are a security incident waiting to happen
5. Performance baselines belong in CI — if P95 regresses >20%, it's a bug, not a metric

Reference Files

• references/tools-and-patterns.md — tool selection table, SuperTest examples, Pact contract testing workflow, schema validation with schemathesis, WireMock and MSW mock server setup, auth token patterns, performance baseline approach
• references/coverage-checklist.md — HTTP scenario coverage checklist (happy path through rate limiting), GraphQL-specific scenarios, error response quality standards, edge cases worth testing