Typescript 和 Jest:避免模拟函数上的类型错误 [英] Typescript and Jest: Avoiding type errors on mocked functions

问题描述

当想用 Jest 模拟外部模块时，我们可以使用 jest.mock() 方法在模块上自动模拟函数.

When wanting to mock external modules with Jest, we can use the jest.mock() method to auto-mock functions on a module.

然后我们可以随意操作和询问模拟模块上的模拟函数.

We can then manipulate and interrogate the mocked functions on our mocked module as we wish.

例如，考虑以下模拟 axios 模块的人为示例:

For example, consider the following contrived example for mocking the axios module:

import myModuleThatCallsAxios from '../myModule';
import axios from 'axios';

jest.mock('axios');

it('Calls the GET method as expected', async () => {
  const expectedResult: string = 'result';

  axios.get.mockReturnValueOnce({ data: expectedResult });
  const result = await myModuleThatCallsAxios.makeGetRequest();

  expect(axios.get).toHaveBeenCalled();
  expect(result).toBe(expectedResult);
});

以上在 Jest 中运行良好，但会抛出 Typescript 错误:

The above will run fine in Jest but will throw a Typescript error:

类型 '(url:字符串，配置?:AxiosRequestConfig |undefined) => AxiosPromise'.

Property 'mockReturnValueOnce' does not exist on type '(url: string, config?: AxiosRequestConfig | undefined) => AxiosPromise'.

axios.get 的 typedef 正确地不包含 mockReturnValueOnce 属性.我们可以通过将 axios.get 包装为 Object(axios.get) 来强制 Typescript 将其视为 Object 字面量，但是:

The typedef for axios.get rightly doesn't include a mockReturnValueOnce property. We can force Typescript to treat axios.get as an Object literal by wrapping it as Object(axios.get), but:

在保持类型安全的同时模拟函数的惯用方法是什么?

What is the idiomatic way to mock functions while maintaining type safety?

推荐答案

添加这行代码const mockedAxios = axios as jest.Mocked.然后使用 mockedAxios 调用 mockReturnValueOnce.使用您的代码，应该这样做:

Add this line of code const mockedAxios = axios as jest.Mocked<typeof axios>. And then use the mockedAxios to call the mockReturnValueOnce. With your code, should be done like this:

import myModuleThatCallsAxios from '../myModule';
import axios from 'axios';

jest.mock('axios');
const mockedAxios = axios as jest.Mocked<typeof axios>;

it('Calls the GET method as expected', async () => {
  const expectedResult: string = 'result';

  mockedAxios.get.mockReturnValueOnce({ data: expectedResult });
  const result = await myModuleThatCallsAxios.makeGetRequest();

  expect(mockedAxios.get).toHaveBeenCalled();
  expect(result).toBe(expectedResult);
});

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