使用 Jest 模拟基于承诺的请求

我正在尝试使用 Jest 对函数进行单元测试，但在处理 jest 模拟模块时遇到了一些麻烦（相当于 Nodejs 世界中的 rewire 或 proxyquire）。

我实际上正在尝试测试是否已使用一些参数在模拟模块上调用了间谍。这是我要测试的功能。

注意：当前测试仅涉及“fetch(...)”部分，我正在尝试测试是否已使用良好的参数调用了 fetch。

export const fetchRemote = slug => {
    return dispatch => {
        dispatch(loading());
        return fetch(Constants.URL + slug)
            .then(res => res.json())
            .then(cmp => {
                if (cmp.length === 1) {
                    return dispatch(setCurrent(cmp[0]));
                }
                return dispatch(computeRemote(cmp));
            });
    };
};

返回的函数充当闭包，因此“捕获”我想要模拟的节点获取外部模块。

这是我试图通过绿色的测试：

it('should have called the fetch function wih the good const parameter and slug', done => {
            const slug = 'slug';
            const spy = jasmine.createSpy();
            const stubDispatch = () => Promise.resolve({json: () => []});
            jest.mock('node-fetch', () => spy);
            const dispatcher = fetchRemote(slug);
            dispatcher(stubDispatch).then(() => {
                expect(spy).toHaveBeenCalledWith(Constants.URL + slug);
                done();
            });
        });

编辑：第一个答案对编写测试有很大帮助，我现在有以下答案：

it('should have called the fetch function wih the good const parameter and slug', done => {
            const slug = 'slug';
            const stubDispatch = () => null;
            const spy = jest.mock('node-fetch', () => Promise.resolve({json: () => []}));
            const dispatcher = fetchRemote(slug);
            dispatcher(stubDispatch).then(() => {
                expect(spy).toHaveBeenCalledWith(Constants.URL + slug);
                done();
            });
        });

但现在，这是我的错误：

 console.error node_modules/core-js/modules/es6.promise.js:117
      Unhandled promise rejection [Error: expect(jest.fn())[.not].toHaveBeenCalledWith()

      jest.fn() value must be a mock function or spy.
      Received:
        object: {"addMatchers": [Function anonymous], "autoMockOff": [Function anonymous], "autoMockOn": [Function anonymous], "clearAllMocks": [Function anonymous], "clearAllTimers": [Function anonymous], "deepUnmock": [Function anonymous], "disableAutomock": [Function anonymous], "doMock": [Function anonymous], "dontMock": [Function anonymous], "enableAutomock": [Function anonymous], "fn": [Function anonymous], "genMockFn": [Function bound getMockFunction], "genMockFromModule": [Function anonymous], "genMockFunction": [Function bound getMockFunction], "isMockFunction": [Function isMockFunction], "mock": [Function anonymous], "resetModuleRegistry": [Function anonymous], "resetModules": [Function anonymous], "runAllImmediates": [Function anonymous], "runAllTicks": [Function anonymous], "runAllTimers": [Function anonymous], "runOnlyPendingTimers": [Function anonymous], "runTimersToTime": [Function anonymous], "setMock": [Function anonymous], "unmock": [Function anonymous], "useFakeTimers": [Function anonymous], "useRealTimers": [Function anonymous]}]

首先，你需要在以下情况下返回一个承诺：测试异步代码 http://facebook.github.io/jest/docs/tutorial-async.html#content。您的间谍需要返回已解决或已拒绝的承诺。

it('should have called the fetch function wih the good const parameter and slug', done => {
  const slug = 'successPath';
  const stubDispatch = () => Promise.resolve({ json: () => [] });
  spy = jest.mock('node-fetch', (path) => {
    if (path === Constants.URL + 'successPath') {
      return Promise.resolve('someSuccessData ')
    } else {
      return Promise.reject('someErrorData')
    }
  });
  const dispatcher = fetchRemote(slug);
  return dispatcher(stubDispatch).then(() => {
    expect(spy).toHaveBeenCalledWith(Constants.URL + slug);
    done();
  });
});