使用 Jest 模拟基于承诺的请求

Question

我正在尝试使用 Jest 对函数进行单元测试，但我在处理 jest 模拟模块（相当于 nodejs 世界中的 rewire 或 proxyquire）时遇到了一些问题。

我实际上是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程序。这是我要测试的功能。

注意：当前测试只涉及 "fetch(...)" 部分，我正在尝试测试是否已使用正确的参数调用 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 "captures" 我要模拟的节点获取外部模块。

这是我试图通过绿色测试的测试：

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();
            });
        });

但是现在，这是我遇到的错误：

 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]}]

Answer 1

首先你需要return一个承诺testing async code。你的间谍需要 return 一个已解决或被拒绝的承诺。

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();
  });
});

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