Mocking node-fetch with jest创建用于mocking的响应对象

Question

我正在尝试创建响应对象，以便使用jest进行模仿，但我似乎无法获得正确的语法。

初始化，

jest.mock('node-fetch')
const fetch = require('node-fetch')
const { Response, Headers } = jest.requireActual('node-fetch')

// Example adapted from https://fetch.spec.whatwg.org/#example-headers-class
const meta = {
  'Content-Type': 'application/json',
  'Accept': '*/*',
  'Breaking-Bad': '<3'
}
// You can in fact use any iterable objects, like a Map or even another Headers
const headers = new Headers(meta)
const copyOfHeaders = new Headers(headers)

const ResponseInit = {
  status: 200,
  statusText: 'fail',
  headers: headers
}

通过基本的测试

  test('Basic Test', async () => {
    const token = ''
    const getDocList = new Response(JSON.stringify(downloadDocumentData), ResponseInit)
    fetch.mockResolvedValueOnce(Promise.resolve(getDocList))
    await module.doSomething('mock', token)
      .then( async(res) => {
        await expect(res.data).toEqual(Object)
      })
  }, 5000)

我收到一个错误，即

     FetchError {
        message:
         'invalid json response body at  reason: Unexpected token H in JSON at position 2',
        type: 'invalid-json' }

我已经尝试了很多不同的方法，如何才能得到有效的json响应呢？

关注https://jestjs.io/docs/en/bypassing-module-mocks上的文章，但我想返回并测试json。

Answer 1

我们应该使用jest.mock(moduleName, factory, options)来模拟node-fetch模块和fetch函数。

为了构造fetch函数的响应对象，您需要使用node-fetch模块提供的Response类，因此使用jest.requireActual(moduleName)获取原始的、未模拟的node-fetch模块和Response类。

当然，我们可以任意构造response对象，但是Response类的实例非常接近真实的响应。

headers对象也是如此。

下面是一个有效的演示：

index.js

const fetch = require('node-fetch');

module.exports = {
  async doSomething(url, token) {
    return fetch(url).then(res => res.json());
  }
};

index.spec.js

jest.mock('node-fetch');

const fetch = require('node-fetch');
const { Response, Headers } = jest.requireActual('node-fetch');
const mod = require('./');

const meta = {
  'Content-Type': 'application/json',
  Accept: '*/*',
  'Breaking-Bad': '<3'
};
const headers = new Headers(meta);
const copyOfHeaders = new Headers(headers);

const ResponseInit = {
  status: 200,
  statusText: 'fail',
  headers: headers
};

test('Basic Test', async () => {
  const token = '';
  const downloadDocumentData = { data: {} };
  const getDocList = new Response(JSON.stringify(downloadDocumentData), ResponseInit);
  fetch.mockResolvedValueOnce(Promise.resolve(getDocList));
  const res = await mod.doSomething('mock', token);
  expect(res).toEqual({ data: {} });
  expect(fetch).toBeCalledWith('mock');
});

单元测试结果：

 PASS  src/stackoverflow/58648691/index.spec.js
  ✓ Basic Test (5ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        2.557s

源代码：https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/58648691