如何使用 jest.fn() 在 jest 中使用 typescript 模拟函数

Question

我正在尝试模拟一个名为 callApi 的函数。我使用 jest.fn()，但我收到错误消息：

function callApi(method: string, url: string, path: string, data?: any): Promise> 无法分配给“callApi”，因为它是只读属性。ts(2540)

我已尝试按照以下示例进行操作 jest examples

我的代码有什么问题？为什么我会收到错误消息。
callApi 的一部分是 从“axios”导入axios；

export function callApi(
  method: string,
  url: string,
  path: string,
  data?: any
) {
  switch (method) {

测试如下：

import {runSaga} from 'redux-saga';
import * as api from '../Utilities/api'
import { getPaymentsError, getPaymentsSuccess, IPaymentsAction } from './actions';
import handleFetch from './sagas'


test('should test fetch payments success',async() =>{
const dispatchedActions = [{}];
const mockedPayments = [{
    details: {
    amount: "10000",
    date: new Date(),
    id: 5
  },
  id: 5,
  month: "Feb 2003",
  userID: 3
}];


 api.callApi = jest.fn(() => Promise.resolve(mockedPayments));<----------error here



const fakeStore = {
    dispatch:(action:IPaymentsAction) =>dispatchedActions.push(action)
}
await runSaga(fakeStore,handleFetch).done;
expect(api.callApi.mock.calls.length).toBe(1);
expect(dispatchedActions).toContainEqual(getPaymentsSuccess(mockedPayments));
})

Answer 1

分配给 jest.fn() 不适用于 TypeScript 输入。

改用jest.spyOn：

test('should test fetch payments success', async (done) => {
  const dispatchedActions = [{}];
  const mockedPayments = [{
    details: {
      amount: "10000",
      date: new Date(),
      id: 5
    },
    id: 5,
    month: "Feb 2003",
    userID: 3
  }];

  const spy = jest.spyOn(api, 'callApi');
  spy.mockImplementation(() => Promise.resolve(mockedPayments));

  const fakeStore = {
    dispatch: (action: IPaymentsAction) => dispatchedActions.push(action)
  }
  await runSaga(fakeStore, handleFetch);done();
  expect(spy.mock.calls.length).toBe(1);
  expect(dispatchedActions).toContainEqual(getPaymentsSuccess(mockedPayments));
})