What is API testing?
API testing sends requests directly to an application’s API and checks the responses, without going through the user interface.
API tests verify status codes, response bodies, schemas, authentication, error handling and performance for each endpoint. Because they skip the browser, they are fast and stable, and they can test cases a UI would never allow.
For products with mobile apps, partners or public APIs, API tests are often the most valuable tests a team owns, because API changes affect clients that cannot be updated instantly.
Example
An API test calls POST /orders with a missing address and checks that the API returns 422 with a clear validation message, not a 500.
Best practices
- Validate every response against the schema
- Test authorization as well as authentication
- Include error and edge cases, not just the happy path
- Chain requests to test real workflows
- Run on every pull request
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