Unable to test post methods with Jest due to error can not read mockImplementation of undefined

Question

I have an api service where I have different methods to make calls to the APIs. I've successfully tested all of the GET requests but I am having troubles testing the POST requests.

This is the method:

export default class ApiService {
  static makeApiCall = <T>(
    url: string,
    oneCb: <T>(d: Data) => T,
    secondCb: (d: T) => void,
    errorCb?: (a: ErrorModel) => void,
    method = 'get',
    data = {},
  ): Promise<void> => {
    const config: AxiosRequestConfig = {};
    if (method === 'post') {
      config.headers = header;
      return ApiClient.post(url, data, config)
        .then(res => callback(normalizeCallback(res.data))).catch(error => someHandler(error));            
    } else {
      return ApiClient.get(url)
        .then(res => callback(normalizeCallback(res.data))).catch(error => someHandler(error));
    }
  };

  // ONLY ONE POST METHOD TO MAKE IT MORE CLEAR
  static someArchiveMethod = (
    callback: (a: SuccessModel) => void,
    errorCallback: (error: ErrorModel) => void,
    cardId: string
  ): Promise<void> => {
    return ApiService.makeApiCall<SuccessfulResponse>(
      'appreciationCard/archive',
      Normalizer.successfulResponse,
      callback,
      errorCallback,
      'post',
      { cardId }
    );
  };

  // HERE BELOW THE GET METHODS
  static getPeople = (cb: (a: PeopleModel[]) => void, page?: number, limit?: number): Promise<void> => {
    const queryDetails = { page, limit };
    return ApiService.makeApiCall<PeopleModel[]>(
      `people?${toQueryString(queryDetails)}`,
      Normalizer.normalizePeople,
      callback
    );
  };
};

This is how I am testing everything related to the GETs:

describe('apiService', () => {
  beforeAll(() => {
    expect(ApiClient.defaults.headers.common.Authorization).toBe('Bearer test token');
    // @ts-ignore
    ApiClient.get.mockImplementation((url: string) => {
      return Promise.resolve({ data: mockData });
    });
  });

  it('should call api client method', () => {
    ApiService.makeApiCall(
      'testUrl',
      data => data,
      res => res,
      err => err,
      'get'
    );

    expect(ApiClient.get).toBeCalledTimes(1);
    expect(ApiClient.get).toBeCalledWith('testUrl');
  });

  it('should call callbacks consequently', done => {
    ApiService.makeApiCall('testUrl', firstCallback, secondCallback).then(() => {
      expect(firstCallback).toBeCalledTimes(1);
      expect(firstCallback).toBeCalledWith(mockData);
      expect(secondCallback).toBeCalledTimes(1);
      expect(secondCallback).toBeCalledWith(firstCallback(mockData));
      done();
    });
  });
});

describe('api service error flow', () => {
  beforeAll(() => {
    // @ts-ignore
    ApiClient.get.mockImplementation((url: string) => {
      console.log('error result');
      return Promise.reject(mockError);
    });
  });

  it('should handle error', done => {
    console.error = jest.fn();

    const firstCallback = jest.fn((data: any) => data);
    const secondCallback = jest.fn((data: any) => data);

    ApiService.makeApiCall('testUrl', firstCallback, secondCallback).then(() => {
      expect(firstCallback).toBeCalledTimes(0);
      expect(secondCallback).toBeCalledTimes(0);
      expect(console.error).toBeCalledTimes(1);
      expect(console.error).toBeCalledWith('ApiClient testUrl', mockError);
      done();
    });
  });
});

describe('apiService methods', () => {
  beforeAll(() => {
    ApiClient.get.mockImplementation((url: string) => {
      expect(ApiClient.defaults.headers.common.Authorization).toBe('Bearer test token');

      return Promise.resolve({ data: mockData });
    });
  });

  it('getPeople method call with one param', () => {
    ApiService.getPeople(jest.fn(), 1, 1).then(() => {
      expect(ApiClient.get).toBeCalledWith('people?page=1&limit=1');
    });
  });
})

I thought that only by changing all of the instances of ApiClient.get to ApiClient.post it will work to test the POST requests. But when I attempt to do that it says that can not read mockImplementation of undefined. I tried changing the methods in the tests to use the post param in order to overwrite the param method = 'get' but I don't have any success, I get this error

TypeError: apiClient_1.default.post is not a function

Any thoughts?

Answer 1

I've investigated your problem. First of all, I want to tell that your code has a couple of issues like calling callback that you didn't define, unclear defining of ApiClient etc.

So, I created a Repl example to reproduce your issue in which I simplified your code a bit but all the main elements are there.

Please, take a look https://repl.it/@SergeyMell/Some-Jesting

It works successfully for both get and post methods with no issues. Here, are the main points you should pay your attention on:

1. Using axios as ApiClient. (It was not clear from your question so I assumed that it is so)

   const ApiClient = require('axios');
   

2. Setting jest mocks on axios (Suppose, you do the same)

   jest.mock('axios');
   

3. Putting mocks to both get and post requests in a similar manner (same to your way)

   ApiClient.get.mockImplementation((url) => {
     return Promise.resolve({ data: mockData });
   });
   
   ApiClient.post.mockImplementation((url) => {
     return Promise.resolve({ data: mockData });
   });
   

So, please, check my example, check the differences with your code and let me know regarding some additional detalization that you may need.