How do the processes of testing user interfaces differ from testing API interfaces?

User interface (UI) testing and API testing differ in goals, methods, and tools.

• UI Testing:

  • Checks visual and interactive elements of the application.
  • Includes verifying element placement, response to user actions (clicks, text input).
  • Often automated using tools like Selenium, Cypress.
  • Tests are more fragile, depend on interface changes.

• API Testing:

  • Checks the correctness of server interfaces (endpoints).
  • Focuses on the accuracy of requests and responses, statuses, data formats.
  • Usually automated with Postman, REST-assured, or built-in tests.
  • Tests are more stable, do not depend on UI.

Example: In UI testing, it is checked whether the "Send" button is visible and clickable, while in API testing, it is verified that a POST request to /submit returns a status 200 and the expected JSON.