QA API Testing and Contracts

Use this skill to turn an API schema into enforceable checks (lint, diff, contracts, and negative/security cases) and wire them into CI so breaking changes cannot ship silently.

Ask For Inputs

• API type and canonical schema artifact (OpenAPI 3.1, SDL, proto) and where it lives in-repo.
• Environments, auth method(s), and how to provision stable test identities/keys.
• Critical endpoints/operations and business flows (rank by risk and revenue impact).
• Data constraints (idempotency keys, pagination, ordering), rate limits, and error format (prefer RFC 7807 application/problem+json for REST).
• Versioning + deprecation policy, consumer inventory, and release cadence.
• Current test tooling/CI and what “blocking” means for your org.

Outputs (What to Produce)

• A minimal CI gate set (lint + breaking diff + contract suite) wired to PRs.
• A coverage map derived from the schema (critical operations first).
• A negative/security baseline aligned to OWASP API risks.

Quick Start

1. Lint the schema (syntax + best-practice rules) and fix issues before writing tests.
2. Add breaking-change checks against the base branch on every PR.
3. Pick a contract strategy (CDC, schema-driven, or both) and run it in CI against an ephemeral environment.
4. Add negative/security cases for auth, validation, and error handling.
5. Make gates explicit (what blocks merge/release) and publish results.

Workflow

1) Establish Contract Artifacts (Source of Truth)

• REST: single OpenAPI 3.1 file or a compiled artifact; avoid drift across fragments.
• GraphQL: checked-in SDL (and federation/composition config if relevant).
• gRPC: checked-in .proto + buf.yaml (or equivalent) with a stable module layout.

2) Validate the Schema (Fast, Deterministic)

• Run spec linting (Spectral / GraphQL Inspector / buf lint).
• Enforce a small, explicit ruleset (naming, descriptions, auth annotations, consistent error model).

3) Detect Breaking Changes (PR Gate)

• REST: OpenAPI diff with a breaking-change policy (remove/rename/type change/requiredness).
• GraphQL: schema diff with breaking checks (field removals, type changes, non-null tightening).
• gRPC: buf breaking (do not reuse/renumber fields; avoid changing request/response shapes incompatibly).

4) Execute Contract Tests (CI Gate)

Choose one or combine:

• CDC (Pact): best when many independent consumers exist and behavior matters beyond schema.
• Schema-driven (Specmatic): best when schema is the contract and you want fast coverage across operations.
• Property-based (Schemathesis): best when you want systematic edge cases and server hardening.

5) Add Negative + Security Cases (Minimum Set)

• AuthN/AuthZ: missing/expired token (401), insufficient scope/role (403), tenant isolation.
• Validation: missing required fields, invalid types, boundary values, empty strings, large payloads.
• Error handling: stable error shape, safe messages, correct status codes, correlation IDs.
• Abuse & limits: rate limiting (429), pagination limits, idempotency replay, retry-safe semantics.
  • For GraphQL, also validate operations checks (known/persisted queries) if you have an operation registry (GraphOS/Hive/etc.).

6) Define CI Quality Gates (Merge + Release)

• Pre-merge: schema lint + breaking-change diff (blocking).
• Pre-release: contract suite (blocking), plus smoke/functional tests for critical flows.
• Reporting: publish artifacts (diff report, contract verification, failing cases) and link in PR.

Quality Checks

• Fail fast: schema violations and breaking changes block merge.
• Determinism: isolate data, freeze time where needed, avoid shared mutable fixtures.
• Flake hygiene: separate network instability from contract failures; retry only for known-transient classes.
• Alignment: contracts reflect versioning/deprecation policy and consumer inventory.
• Scope control: keep load/resilience tests separate unless explicitly requested.

Use the Bundled Templates

• Coverage plan: assets/api-test-plan.md
• Release review: assets/contract-change-checklist.md
• Tooling map: assets/schema-validation-matrix.md

AI Assistance (Use Carefully)

• Use AI to draft tests, suggest missing edge cases, and tighten matchers.
• Treat AI output as untrusted until verified against the schema and real behavior.
• Avoid uploading sensitive payloads; sanitize examples and logs.
• For a tool comparison and workflows, read references/ai-contract-testing.md.

Read These When Needed

• Change safety and CDC patterns: references/contract-testing-patterns.md
• AI-assisted tooling and decision matrix: references/ai-contract-testing.md
• Curated authoritative links: data/sources.json

Related Skills

• Use dev-api-design for API design decisions.
• Use qa-testing-strategy for overall testing strategy.
• Use qa-resilience for chaos and reliability testing.
• Use software-security-appsec for API security review.