API Testing
Verifying an API's behavior directly, without going through a UI.
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Overview
API testing verifies a backend's behavior (status codes, response shape, error handling) by calling it directly, without a browser or UI in the loop -- faster and more stable than UI tests for verifying backend logic specifically.
- What it is
- Testing an API's requests and responses directly, independent of any UI.
- Why it's used
- It's faster and less brittle than testing the same logic through a UI, and catches backend bugs closer to their source.
- Where it fits
- Complements UI-level testing (Selenium/Playwright); often the majority of a backend team's automated test suite. The API Testing and Automation course covers this in depth: schema validation, positive/negative testing, chained workflows, security basics, and automation structure.
Core concepts
- Asserting status codes
- Asserting response body shape
- Testing error cases, not just the happy path
- Test data setup and teardown
Example
Testing the error path (a 404 for a nonexistent resource) matters as much as testing the success path -- a common gap in under-tested APIs.
const res = await fetch("/api/books/999"); // a nonexistent book
console.assert(res.status === 404, "Expected 404 for missing book");Common use cases
- Verifying backend behavior independent of any frontend
- Catching regressions in API contracts
Project ideas
- Write a handful of assertions against a small REST API's endpoints, covering both success and error cases