Jest Intermediate Quiz
Explore mocking, async testing, snapshot testing, coverage, and test organization
Start the quizSample questions from this quiz
A preview of the style and depth. Try each one, then reveal the answer — or skip straight to the timed quiz.
1. What is mocking in Jest?
- Replacing real implementations with test versions
- Test doubles
- Fake data
- Simulation
Show answer
Answer: Replacing real implementations with test versions. Mocking replaces real implementations with controllable test versions. Isolate code under test, control dependencies, verify interactions. Use jest.fn(), jest.mock().
2. What is jest.fn()?
- Spy function
- Test function
- Function mocker
- Creates mock function
Show answer
Answer: Creates mock function. jest.fn() creates mock function. Track calls, arguments, return values. Can provide implementation. Example: const mockFn = jest.fn(); mockFn(); expect(mockFn).toHaveBeenCalled().
3. How do you check if mock was called?
- expect(mockFn).toHaveBeenCalled()
- mockFn.wasCalled()
- expect(mockFn).called()
- mockFn.called === true
Show answer
Answer: expect(mockFn).toHaveBeenCalled(). Check calls with toHaveBeenCalled(). Also: toHaveBeenCalledTimes(n), toHaveBeenCalledWith(args), toHaveBeenLastCalledWith(args).
Frequently asked questions
How many questions are in this Jest quiz?+
30 questions, with a 60-minute time limit. Every question includes a written explanation of the correct answer.
Is this Jest quiz free?+
Yes. Every quiz on CodexQuizz is free and needs no account. You only enter a name if you choose to post your score to the leaderboard.
What level is the intermediate quiz aimed at?+
Explore mocking, async testing, snapshot testing, coverage, and test organization
Can I use this to prepare for a Jest interview?+
Yes. The questions cover the topics that come up in Jest technical screens, and the explanations are written so that a wrong answer still teaches you the underlying concept.
Ready to test your Jest?
30 questions, 60 minutes. Free, no sign-up.
Start now