开玩笑 es6 class 模拟返回未定义

Question

I have a simple class that I want to mock and for some reason jest returns undefined.

Here's the code:

import { MyClass as myClass } from './my-class'; 
jest.mock('./my-class', () => jest.fn());
console.log(myClass); // undefined

When I log myClass I get undefined .

If I mock without mocking the implementation, I get this:

import { MyClass as myClass } from './my-class'; 
jest.mock('./my-class');
console.log(myClass);

The code above logs: function MyClass() {return mockConstructor.apply(this,arguments);}

Which does not allow for mocking, since it is not a jest.fn() and it has none of the useful methods like mockImplementation .

What is the right way to do it?

Answer 1

You didn't mock the my-class module correctly. You are using Named Exports , you also need to mock this.

Eg

my-class.ts :

export class MyClass {}

my-class.test.ts :

import { MyClass as myClass } from './my-class';
jest.mock('./my-class', () => ({ MyClass: jest.fn() }));
console.log(myClass);

Output:

  console.log
    { [Function: mockConstructor]
      _isMockFunction: true,
      getMockImplementation: [Function],
      mock: [Getter/Setter],
      mockClear: [Function],
      mockReset: [Function],
      mockRestore: [Function],
      mockReturnValueOnce: [Function],
      mockResolvedValueOnce: [Function],
      mockRejectedValueOnce: [Function],
      mockReturnValue: [Function],
      mockResolvedValue: [Function],
      mockRejectedValue: [Function],
      mockImplementationOnce: [Function],
      mockImplementation: [Function],
      mockReturnThis: [Function],
      mockName: [Function],
      getMockName: [Function] }