Quiz for Jest Basics

Q1: What is Jest primarily used for in React development?

A. A. Unit testing B. B. Styling components C. C. Routing D. D. State management

Q2: Which command runs tests using Jest in a React project?

A. A. npm test B. B. npm start C. C. npm build D. D. npm install

Q3: Which function is used to group related tests in Jest?

A. A. describe() B. B. test() C. C. it() D. D. expect()

Q4: How do you write a single test case in Jest?

A. A. test() B. B. expect() C. C. describe() D. D. render()

Q5: Which function asserts the expected outcome in Jest?

A. A. expect() B. B. test() C. C. describe() D. D. render()

Q6: What does the Jest matcher .toBe() check?

A. A. Strict equality (===) B. B. Object equality C. C. Array length D. D. Function call

Q7: Which Jest function is used to clean up mocks between tests?

A. A. jest.clearAllMocks() B. B. jest.runAllTimers() C. C. jest.resetModules() D. D. jest.mock()

Q8: How do you mock a module in Jest?

A. A. jest.mock("moduleName") B. B. jest.spyOn() C. C. jest.clearAllMocks() D. D. jest.resetModules()

Q9: What is a snapshot test in Jest?

A. A. Captures rendered output to detect changes B. B. Tests API responses C. C. Tests form input D. D. Tests database calls

Q10: How do you update a Jest snapshot?

A. A. Run tests with -u or --updateSnapshot flag B. B. Manually edit files C. C. Reinstall Jest D. D. Change test names

Q11: Which of these is a common testing utility used with Jest in React?

A. A. React Testing Library B. B. Express C. C. Axios D. D. Redux

Q12: What does the .toHaveBeenCalled() matcher verify?

A. A. If a mock function was called B. B. If a component rendered C. C. If a function returns a value D. D. If a variable is defined

Q13: What is the purpose of jest.fn()?

A. A. Creates a mock function B. B. Defines a new component C. C. Styles components D. D. Handles API requests

Q14: Which lifecycle method is commonly tested with Jest in class components?

A. A. componentDidMount B. B. render C. C. constructor D. D. shouldComponentUpdate

Q15: How do you test asynchronous code with Jest?

A. A. Using async/await or done callback B. B. Only synchronous testing C. C. Using setTimeout D. D. Not possible

Q16: What Jest configuration file is commonly used to customize Jest?

A. A. jest.config.js B. B. package.json C. C. webpack.config.js D. D. babel.config.js

Q17: How can you run only one test in Jest?

A. A. Use test.only() B. B. Use test.skip() C. C. Use describe() D. D. Use it.skip()

Q18: What is the role of jest.setup.js?

A. A. Setup file to run before tests B. B. Runs after tests C. C. Contains all tests D. D. Used for styling

Q19: Which command runs Jest tests in watch mode?

A. A. npm test -- --watch B. B. npm run build C. C. npm start D. D. npm install

Q20: What does the .toContain() matcher do?

A. A. Checks if array or string contains a value B. B. Checks number equality C. C. Checks function calls D. D. Checks component render