jest.mock(): How to mock ES6 class default import using factory parameter

Question

Mocking ES6 class imports

I\'d like to mock my ES6 class imports within my test files.

If the class being mocked has multiple consumers, it may make sense

Answer 1

If you are still getting TypeError: ...default is not a constructor and are using TypeScript keep reading.

TypeScript is transpiling your ts file and your module is likely being imported using ES2015s import. const soundPlayer = require('./sound-player'). Therefore creating an instance of the class that was exported as a default will look like this: new soundPlayer.default(). However if you are mocking the class as suggested by the documentation.

jest.mock('./sound-player', () => {
  return jest.fn().mockImplementation(() => {
    return { playSoundFile: mockPlaySoundFile };
  });
});

You will get the same error because soundPlayer.default does not point to a function. Your mock has to return an object which has a property default that points to a function.

jest.mock('./sound-player', () => {
    return {
        default: jest.fn().mockImplementation(() => {
            return {
                playSoundFile: mockPlaySoundFile 
            }   
        })
    }
})

For named imports, like import { OAuth2 } from './oauth', replace default with imported module name, OAuth2 in this example:

jest.mock('./oauth', () => {
    return {
        OAuth2: ... // mock here
    }
})