Jest spyOn() calls the actual function instead of the mocked

I’m testing apiMiddleware that calls its helper function callApi. To prevent the call to actual callApi which will issue the api call, I mocked the function. However, it still gets called.

apiMiddleware.js

import axios from 'axios';

export const CALL_API = 'Call API';

export const callApi = (...arg) => {
  return axios(...arg)
  	.then( /*handle success*/ )
  	.catch( /*handle error*/ );
};

export default store => next => action => {
  // determine whether to execute this middleware
  const callAPI = action[CALL_API];
  if (typeof callAPI === 'undefined') {
    return next(action)
  }

  return callAPI(...callAPI)
  	.then( /*handle success*/ )
  	.catch( /*handle error*/ );
}

apiMiddleware.spec.js

import * as apiMiddleware from './apiMiddleware';

const { CALL_API, default: middleware, callApi } = apiMiddleware;

describe('Api Middleware', () => {

  const store = {getState: jest.fn()};
  const next = jest.fn();
  let action;

  beforeEach(() => {
    // clear the result of the previous calls
    next.mockClear();
    // action that trigger apiMiddleware
    action = {
      [CALL_API]: {
        // list of properties that change from test to test 
      }
    };
  });

  it('calls mocked version of `callApi', () => {
	const callApi = jest.spyOn(apiMiddleware, 'callApi').mockReturnValue(Promise.resolve());

	// error point: middleware() calls the actual `callApi()` 
	middleware(store)(next)(action);

	// assertion
  });
});

Please ignore the action’s properties and argument of callApi function. I don’t think they are the concern of the point I’m trying to make.

Tell me if you need further elaboration.

stackoverflow

[rickhanlonii]

@NERDYLIZARD sorry for the delay here!

By default jest.spyOn() does not override the implementation (this is the opposite of jasmine.spyOn). If you don’t want it to call through you have to mock the implementation:

const callApi = jest.spyOn(apiMiddleware, 'callApi').mockImplementation(() => Promise.resolve());

[JonathanHolvey]

I seem to be having this problem as well, but the solution that @rickhanlonii proposed isn’t working for me. I’m following the documentation for jest.spyOn(), but the mocked function is still being called when running the tests.

processing.js

const saveVisit = (visit) => {
  return database.put(visit)
}

const processVisit = (visit) => {
  if (visit.status.includes('PROCESSED') {
    saveVisit(visit)
    return promise.resolve()
  }

  saveVisit({ ...visit, status: ['PROCESSED'] })
  return visit.status
}

processing.test.js

const subject = require('../processing')

test('processVisit for processed visit returns null', () => {
  const visit = { status: ['PROCESSED'] }

  jest.spyOn(subject, 'saveVisit').mockImplementation(() => Promise.resolve())
  return subject.processVisit(visit).then(result => expect(result).toBeNull())
})