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API testing

API testing is a type of software testing that verifies the Application Programming Interface (API) of an application to ensure it meets expectations for functionality, reliability, performance, and security.

It involves sending requests to an API's endpoints and validating the responses against expected outcomes. This testing focuses on the business logic and data layer of an application, bypassing the User Interface (UI). Therefore the UI behaviour of an application cannot be tested via API testing.

1. How to Set Up an API Test​

Setting up an API test involves a structured process, from understanding the API contract to executing and verifying the results.

  1. Understand API documentation and requirements: Before writing any tests, you must fully understand the API's specifications (e.g. endpoints, HTTP Methods, request/response format, authentication/authorization, status codes,…).
  2. Define test scenarios and cases: Create a comprehensive plan of what you need to test with at least: positive and negative scenarios (Error Handling), edge cases and security tests.
  3. Choose a tool and configure the test environment: Select an appropriate tool and configure the testing environment.
  4. Build test scripts and execute the test: The test scripts should run correctly against the test environment and should be repeatable.
  5. Add asserts to the response: This is the core of API testing, where you verify that the actual response meets all expected conditions.