如何验证在打字稿单元测试中调用了node-fetch？

如何解决如何验证在打字稿单元测试中调用了node-fetch？

嗨，我有一个导出一些方法的模块，我想用一些单元测试来测试它们。我的项目基于打字稿^ 3.9.7，并安装了jest ^ 26.1.0和ts-jest ^ 26.2.0

其中一种方法可以导入node-fetch ^ 2.6.0，以便能够在节点环境中使用window.fetch。

import fetch from 'node-fetch'

export const fetchResponseFromRemoteFile = (
  remoteFileUrl: string
): Promise<Response> =>
  fetch(remoteFileUrl)
    .then(res => {
      return res.status === 200
        ? res
        : new Error(`failed to retrieve ${remoteFileUrl}`)
    })
    .catch(e => e)

在我的一项测试中，我想检查 fetchResponseFromRemoteFile 是否调用 fetch

方法1

import { mocked } from 'ts-jest/utils'
import fetch from 'node-fetch'

jest.mock('node-fetch')

it('fetches',async () => {  
  const expectedResponse = { a: 1 }
  mocked(fetch).mockImplementation( () => <any>expectedResponse)
  ...
})


// mocked(fetch).mockImplementation( () => <any>expectedResponse)

TypeError: (0,_utils2.mocked)(...).mockImplementation is not a function

方法2

it('fetches',async () => {
  const expectedResponse = { a: 1 }
  ;(fetch as jest.Mock).mockReturnValue(Promise.resolve(new Response(expectedResponse)))
  const remoteFile = await utils.fetchResponseFromRemoteFile(mockUrl)
  expect(fetch).toHaveBeenCalledTimes(1)
  expect(remoteFile.status).toEqual(200);
  expect(remoteFile.body).toEqual(expectedResponse);
  ...
})


// ;(fetch as jest.Mock).mockReturnValue(Promise.resolve(new Response(expectedResponse)))

ReferenceError: Response is not defined

方法3

import fetch from 'node-fetch'

jest.mock('node-fetch',() => jest.fn())

it('fetches',async () => {
  const expectedResponse = { body: { a: 1 } }
  const response = Promise.resolve(expectedResponse)
  fetch.mockImplementation(()=> response)
  ...
})


// fetch.mockImplementation(()=> response)

TypeError: _nodeFetch.default.mockImplementation is not a function

关于这里发生的事情的想法？ 预先感谢

解决方法

要对此进行正确的单元测试，应使用依赖项注入：

export class FetchService {

  constructor(private readonly fetchInstance: any) {}

  public fetchResponseFromRemoteFile(
    remoteFileUrl: string
  ): Promise < Response > {
    this.fetchInstance(remoteFileUrl)
        .then(res => {
            return res.status === 200
                ? res
                : new Error(`failed to retrieve ${remoteFileUrl}`)
        })
        .catch(e => e);
  }
}

这样，您可以实例化一个模拟并将其传递给您的服务，同时进行如下测试：

const fetchMock = jest.Mock(); // Don't know the exact code but you know what I mean
const fetchService = new FetchService(fetchMock);

// Now you can do assertions on the 'fetchMock'.