javascript - 我如何用 Jest 来模拟异步提取？

Question

几天来我一直在努力想办法正确地测试这段代码:(

const request = require('superagent');

const getDog = () => {
  return request.get('https://dog.ceo/api/breeds/image/random');
};

it('resolves', () => {
  // Expect mocked response
});

it('rejects', () => {
  // Expect mocked response
});

Answer 1

在大多数情况下，您的代码会从 API 中获取一些值，然后对其进行解析并使用它来制作一些东西。
因此，您不想进行真正的 API 调用而是模拟它。
有几种方法可以做到这一点。一种可能是模拟 superagent 库中的唯一方法。

// tell jest not to mock superagent because we'll mock the only method
jest.unmock('superagent');

const request = require('superagent');

const getDog = () => {
  return request.get('https://dog.ceo/api/breeds/image/random');
};

it('resolves', () => {
  // mock the get request to resolve object
  request.get = jest.fn().mockResolvedValue({
  message: 'Your message'
  });
  // Expect mocked response
  expect.assertions(1);
  return expect(getDog()).resolves.toEqual({
  message: 'Your message'
  });
});

it('rejects', () => {
  // mock the get request to reject object
  request.get = jest.fn().mockRejectedValue({
  message: 'Your error'
  });
  // Expect mocked response
  expect.assertions(1);
  return expect(getDog()).rejects.toEqual({
    message: 'Your error'
  });
});

我使用了expect.assertions(1)，有一个reason :

This is often useful when testing asynchronous code, in order to make sure that assertions in a callback actually got called.

有些链接可以帮助您: mockFn.mockResolvedValue(value) , .rejects