What tests have you written on the backend? What libraries did you use?

On the backend, several types of tests were usually written:

• Unit tests for checking individual functions and modules. Libraries like Jest or Mocha were used.
• Integration tests for verifying interactions between components, such as with databases or external services.
• E2E tests (end-to-end) for testing the entire application.

The following libraries were often used:

• Jest — a popular testing framework with support for mocks and asynchronous operations.
• Supertest — for testing HTTP requests to APIs.
• Sinon — for creating mocks, stubs, and spies.

Example of a simple unit test with Jest:

const sum = (a, b) => a + b;

test('adds 1 + 2 to equal 3', () => {
  expect(sum(1, 2)).toBe(3);
});

For integration tests, a test database is often set up or in-memory solutions are used.