当使用“doMock”避免吊装时，Jest不会嘲笑模块

Question

I'm trying to mock a class that creates and returns another class. I've got this:

const mockMethod = jest.fn();

const mockClassA = jest.fn<ClassA>(() => ({
  method: mockMethod
}));

jest.mock("../src/ClassB", () => ({
  ClassB: {
    getClassA: () => new mockClassA()
  }
}));

It gets caught out because of the hoisting, the mockClassA is undefined when jest is mocking `../src/ClassB".

I've read if you don't want hoisting, just use doMock instead:

When using babel-jest, calls to mock will automatically be hoisted to the top of the code block. Use this method if you want to explicitly avoid this behavior.

https://jestjs.io/docs/en/next/jest-object#jestdomockmodulename-factory-options

When I run with mock , I get TypeError: mockClassA is not a constructor , as mockClassA is undefined because the mock is hoisted above the definition for mockClassA.

When I change mock to doMock , it simply does not mock the module - it uses the real thing.

---

Edit: Declairing them in-line means I can't easily access the mocked methods for checking:

jest.mock("../src/ClassB", () => ({
  ClassB: {
    getClassA: () => ({
      method: jest.fn()
    })
  }
}));

Because getClassA is a function, it's returning a separate instance of the object with method .

---

Edit 2: Ah! Managed to inline it like so:

jest.mock("../src/ClassB", () => {
  const mockMethod: jest.fn();
  return {
    ClassB: {
      getClassA: () => ({
        method: mockMethod
      })
    }
  };
});

Answer 1

I think you have 2 options here:

1. use jest.mock , inline the mockClassA and mockMethod , expose them in the mock and then import from '../src/ClassB'
2. use doMock, but use a dynamic require within your test case.