Mock.mockImplementation() not working

I had same problem as @Janos, the other answers didn’t help either. You could do two things :

1. If you need to mock only a function from Service, in your test file:

   import service from './Service';
   
   jest.mock('./Service', () => jest.fn());
   
   service.yourFunction = jest.fn(() => { /*your mock*/ })
   

    

2. If you need to mock the entire Module:

   Say your service.js is in javascript/utils, create a javascript/utils/_mocks_ and inside it create a service.js file, you can then mock the entire class in this file, eg:

   const myObj = {foo: "bar"}
   
   const myFunction1 = jest.fn(() => { return Promise.resolve(myObj) })
   
   const  myFunction2 = ...
   
   module.exports = {
     myFunction1,
     myFunction2
   }
   

   then in your test file you just add:

   jest.mock('./javascript/utils/service')
   

   …functions exported from the mockfile will be then hit through your test file execution.