如何使用 Jest 模拟 ES6 模块导入? [英] How can I mock an ES6 module import using Jest?

问题描述

我想测试我的 ES6 模块之一以特定方式调用另一个 ES6 模块.使用 Jasmine 这非常简单 --

I want to test that one of my ES6 modules calls another ES6 module in a particular way. With Jasmine this is super easy --

应用代码:

// myModule.js
import dependency from './dependency';

export default (x) => {
  dependency.doSomething(x * 2);
}

和测试代码:

//myModule-test.js
import myModule from '../myModule';
import dependency from '../dependency';

describe('myModule', () => {
  it('calls the dependency with double the input', () => {
    spyOn(dependency, 'doSomething');

    myModule(2);

    expect(dependency.doSomething).toHaveBeenCalledWith(4);
  });
});

Jest 的等价物是什么?我觉得这是一件很简单的事情，但我一直在努力弄清楚.

What's the equivalent with Jest? I feel like this is such a simple thing to want to do, but I've been tearing my hair out trying to figure it out.

我最接近的是用 requires 替换 imports，并将它们移动到测试/函数中.这两件事我都不想做.

The closest I've come is by replacing the imports with requires, and moving them inside the tests/functions. Neither of which are things I want to do.

// myModule.js
export default (x) => {
  const dependency = require('./dependency'); // Yuck
  dependency.doSomething(x * 2);
}

//myModule-test.js
describe('myModule', () => {
  it('calls the dependency with double the input', () => {
    jest.mock('../dependency');

    myModule(2);

    const dependency = require('../dependency'); // Also yuck
    expect(dependency.doSomething).toBeCalledWith(4);
  });
});

对于奖励积分，当 dependency.js 中的函数是默认导出时，我很乐意让整个事情正常工作.但是，我知道监视默认导出在 Jasmine 中不起作用(或者至少我永远无法让它工作)，所以我也不希望在 Jest 中也可以这样做.

For bonus points, I'd love to make the whole thing work when the function inside dependency.js is a default export. However, I know that spying on default exports doesn't work in Jasmine (or at least I could never get it to work), so I'm not holding out hope that it's possible in Jest either.

推荐答案

快进到 2020 年，我发现这篇博文是解决方案:Jest mock 默认和命名导出

Fast forwarding to 2020, I found this blog post to be the solution: Jest mock default and named export

仅使用 ES6 模块语法:

Using only ES6 module syntax:

// esModule.js
export default 'defaultExport';
export const namedExport = () => {};

// esModule.test.js
jest.mock('./esModule', () => ({
  __esModule: true, // this property makes it work
  default: 'mockedDefaultExport',
  namedExport: jest.fn(),
}));

import defaultExport, { namedExport } from './esModule';
defaultExport; // 'mockedDefaultExport'
namedExport; // mock function

还有一件事你需要知道(我花了一段时间才弄明白)是你不能在测试中调用 jest.mock() ；您必须在模块的顶层调用它.但是，如果您想为不同的测试设置不同的模拟，您可以在各个测试中调用 mockImplementation().

Also one thing you need to know (which took me a while to figure out) is that you can't call jest.mock() inside the test; you must call it at the top level of the module. However, you can call mockImplementation() inside individual tests if you want to set up different mocks for different tests.

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