Tell me about testing the client-side of the application.

Client-side testing (frontend) includes several levels:

• Unit tests: check individual components or functions, such as React components or utilities. Usually written using Jest, Mocha.

• Integration tests: verify interaction between multiple components or modules.

• UI tests: check the display and behavior of the interface, for example, using libraries like Testing Library.

• E2E (end-to-end) tests: simulate user actions in the browser, testing the entire application. Tools like Selenium, Cypress, Playwright are used.

Test automation helps quickly identify errors when code changes. It is important to cover critical paths and user scenarios to ensure stability and quality of the interface.