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Testing Notes

1. Jest

Jest is a JavaScript testing framework commonly used for unit and integration testing.

Core Ideas

  • tests verify expected behavior
  • assertions compare expected vs actual
  • mocks isolate dependencies

Common Features

  • test runners
  • matchers
  • spies
  • mocks
  • snapshots

Example

test("adds numbers", () => {
  expect(2 + 2).toBe(4);
});

Jest Notes

  • keep tests small and focused
  • test behavior, not implementation details
  • mock external dependencies when needed

2. Supertest

Supertest is used to test HTTP servers and Express routes.

Why It Helps

  • sends requests to your app in tests
  • checks status codes and responses
  • works well with Jest

Example

request(app)
  .get("/users")
  .expect(200);

Supertest Notes

  • useful for API route testing
  • good for integration testing of Express endpoints
  • often paired with a test database or mock server

3. React Testing Library

React Testing Library focuses on testing components the way users interact with them.

Core Philosophy

  • test what users see and do
  • avoid testing internal implementation details when possible

Common Queries

  • by text
  • by role
  • by label text
  • by placeholder
  • by test id as a fallback

Example

render(<Button />);
screen.getByRole("button", { name: /save/i });

RTL Notes

  • prefer accessible queries
  • simulate user behavior
  • assert visible outcomes
  • keep tests close to real usage