API Testing: Tools and Strategies
API testing validates that your API behaves correctly — returning expected responses, handling edge cases, enforcing authentication and authorisation, and meeting performance requirements. A comprehensive API testing strategy catches bugs before production and provides confidence that API changes don't break existing consumers.
Types of API Tests
- Functional tests: Does the API return the correct response for valid requests? Does it handle invalid inputs correctly? Does it enforce authorisation?
- Contract tests: Does the API response match the published schema? Used to detect breaking changes before consumers are affected.
- Integration tests: Do multiple API calls in sequence produce correct results? Do cross-service interactions work correctly?
- Performance tests: Does the API meet latency requirements under load?
- Security tests: Are authentication and authorisation enforced? Are injection attacks rejected? Are sensitive data fields correctly protected?
API Testing Tools
- Postman / Insomnia: GUI tools for manual API exploration and automated test collections
- REST Assured (Java): Fluent Java library for REST API testing — popular in Java ecosystems
- Supertest (Node.js): HTTP testing library for Node.js — integrates with Jest and Mocha
- pytest + httpx / requests (Python): Python HTTP testing
- Hurl: Text-based HTTP testing tool — tests as plain-text files, easy to version control
Automated API Testing in CI/CD
API tests should run automatically on every commit. Fast unit-level API tests in the main CI pipeline; longer integration tests in a separate stage. Fail the build on API test failures — the same standard as any other test failure.