如何模拟从第三方库导出的类？

Question

我们正在使用 Jest 为 React 组件编写一些单元测试，我遇到了一个我似乎无法解决的问题。我们需要从导出多个类的第三方库中模拟单个类。但我们不想模拟所有的类，而只是模拟一个类。

// third-party-library
export ClassA;
export ClassB;
export ClassC;

// hooks.js
import { useState } from 'react';
import { ClassB } from 'third-party-module';

export const myHook = () => {
  const [mystate, setMystate] = useState({});
  const classB = new ClassB();
  // ...implementation...
  return mystate;
};

// our-test-case.js
import { myHook } from '../hooks.js';

// --- This isn't quite what I want (ClassA and ClassC are mocked)
// jest.mock('third-party-library');
// ---

// --- This also does not appear to work (ClassA and ClassC are still mocked)
// jest.mock('third-party-library', () => ({
//   __esModule: true,
//   ClassB: class {
//     ...mock implementation..
//   }
// });
// ---

it('mock ClassB', () => {
  const mystate = myHook();
  // ...implementation...
});

我只想ClassB在这个例子中嘲笑。我想保持ClassA相同ClassC（此文件中还有其他测试依赖于它。我做错了什么？

Answer 1

经过更多挖掘笑话文档和反复试验后，我找到了金块。这是最终的测试用例代码：

// our-test-case.js
import { myHook } from '../hooks.js';

jest.mock('third-party-library', () => ({
  __esModule: true,
  ...jest.requireActual('third-party-library'), // This is the golden nugget.
  ClassB: class {
    ...mock implementation..
  }
});

it('mock ClassB', () => {
  const mystate = myHook();
  // ...implementation...
});

参考： https: //jestjs.io/docs/en/bypassing-module-mocks