API testing verifies that backend endpoints behave as expected.

It helps identify issues before the application reaches production.

Common API testing categories include:

Unit testing

Tests individual functions or modules in isolation.

Integration testing

Tests how multiple application components work together.

End-to-end testing

Tests complete application workflows through the public interface.

For our REST API, we will use Supertest to send HTTP requests directly to the Express application.

We will use Jest as the test runner.

Because the application uses ES Modules, Jest requires compatible configuration.