MCQs on Testing in TypeScript | TypeScript

Explore the world of TypeScript testing with these 30 multiple-choice questions. Understand how to write tests with Jest and Mocha, type test cases, and effectively use mocking and stubbing in TypeScript.

Topic 1: Writing Tests with Jest or Mocha (10 Questions)

1. Which of the following is the correct way to import Jest in a TypeScript test file?
   A) import { jest } from 'jest';
   B) import * as jest from 'jest';
   C) import jest from 'jest';
   D) import { expect, jest } from 'jest';
2. Which command is used to install Jest in a TypeScript project?
   A) npm install jest --save-dev
   B) npm install @jest/types
   C) npm install jest-ts
   D) npm install typescript jest
3. How can you add TypeScript support to Jest?
   A) By adding ts-jest as a transformer in the Jest configuration
   B) By setting the module property to commonjs
   C) By using Babel for TypeScript files
   D) By setting "tsSupport": true in Jest configuration
4. Which Mocha method is used to start a test suite?
   A) describe()
   B) test()
   C) suite()
   D) start()
5. What is the correct syntax to define a test case in Mocha?
   A) it('should return true', () => { ... })
   B) test('should return true', () => { ... })
   C) expect('should return true').toEqual()
   D) describe('should return true', () => { ... })
6. In Jest, how would you create a mock function?
   A) jest.fn()
   B) mockFunction()
   C) jest.mock()
   D) mockFunction.create()
7. Which of the following is a valid assertion method in Jest?
   A) assert.equals(value1, value2)
   B) assertSame(value1, value2)
   C) expect(value).toBe(value)
   D) should(value).equal(value)
8. What is the default test runner used by Jest?
   A) Karma
   B) Jasmine
   C) Mocha
   D) Jest Runner
9. Which of the following is the purpose of the beforeEach() method in Jest or Mocha?
   A) To execute code before each test case runs
   B) To run the tests in parallel
   C) To clean up after each test case
   D) To configure the test suite settings
10. In Mocha, which method is used to handle asynchronous code in a test case?
    A) done()
    B) async()
    C) await
    D) next()

Topic 2: Typing Test Cases (10 Questions)

11. What is the correct way to type a Jest test function in TypeScript?
    A) test('description', () => { ... })
    B) test<string>('description', () => { ... })
    C) it('description', () => { ... })
    D) test('description', (value: string) => { ... })
12. How do you type a mock function in Jest that accepts a number and returns a string?
    A) jest.fn<(number) => string>()
    B) jest.fn() as jest.Mock<(number) => string>
    C) jest.fn<(string) => number>()
    D) jest.mock<(number) => string>
13. How can you type the result of a beforeEach() method in Mocha?
    A) By typing the return value in the function signature
    B) By typing the done callback
    C) By using any for the return type
    D) There’s no need to type beforeEach()
14. How can you assert that a value is of type string in Jest?
    A) expect(value).toBeString()
    B) expect(value).toHaveType('string')
    C) expect(typeof value).toBe('string')
    D) expect(value).toBeOfType('string')
15. In TypeScript, how do you type a test suite function?
    A) describe('Test Suite', (): void => { ... })
    B) describe('Test Suite', (value: string): void => { ... })
    C) describe('Test Suite', () => { ... })
    D) describe('Test Suite', (): any => { ... })
16. What is the correct way to type an array of test results in Jest?
    A) let results: string[] = []
    B) let results: Array<string> = []
    C) let results: TestResult[] = []
    D) let results: any[] = []
17. How can you type the return value of a Jest mock function that returns boolean?
    A) jest.fn<boolean>()
    B) jest.fn(() => true)
    C) jest.Mock<boolean>
    D) jest.fn<boolean>().mockReturnValue(true)
18. What is the correct type to use for a callback in Mocha’s beforeEach method?
    A) () => void
    B) () => Promise<void>
    C) (done: () => void) => void
    D) (done: any) => void
19. How can you type a spy function in Jest?
    A) jest.spyOn()
    B) jest.fn()
    C) jest.mock()
    D) jest.spyOn(fn, 'method')
20. In TypeScript, how can you type an object that holds test data?
    A) let data: Record<string, string>
    B) let data: object
    C) let data: any[]
    D) let data: TestData[]

Topic 3: Mocking and Stubbing in TypeScript (10 Questions)

21. What is the purpose of mocking in TypeScript tests?
    A) To simulate real objects for testing
    B) To execute tests faster
    C) To prevent errors in tests
    D) To optimize test code
22. How can you mock an HTTP request in Jest?
    A) Using jest.fn() to create a mock function
    B) By using jest.spyOn() on the HTTP method
    C) By using mockResolvedValue() to simulate a response
    D) All of the above
23. How do you stub a method in Mocha for testing?
    A) By replacing the method with a fake implementation
    B) By using sinon.stub()
    C) By using jest.spyOn()
    D) By using mockReturnValue()
24. What is the advantage of using spies in TypeScript tests?
    A) To track method calls and arguments
    B) To simulate missing methods
    C) To measure performance of methods
    D) To isolate external dependencies
25. How can you mock a specific class method in Jest?
    A) jest.spyOn(Class, 'method')
    B) jest.fn(Class.method)
    C) mockFunction(Class.method)
    D) jest.mock(Class.method)
26. Which function can be used to mock an entire module in Jest?
    A) jest.fn()
    B) jest.mock()
    C) jest.stub()
    D) jest.spyOn()
27. How do you mock a value that is returned from a function in Jest?
    A) jest.mockReturnValue()
    B) jest.fn().mockReturnValue()
    C) mockReturn()
    D) jest.setMock()
28. How can you mock a method with multiple arguments in Jest?
    A) jest.fn().mockImplementation((arg1, arg2) => { ... })
    B) jest.fn().mockReturnValue()
    C) jest.spyOn().mockImplementation()
    D) jest.fn().mockArgs()
29. What method in Mocha is used for stubbing object properties?
    A) sinon.stub()
    B) jest.stub()
    C) sinon.spy()
    D) mock.stub()
30. How do you use Jest to mock an imported module in TypeScript?
    A) jest.mock('./module')
    B) jest.spyOn('./module')
    C) mockImport('./module')
    D) jest.fn('./module')

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