How to write test cases to cover all the nested 'then' callbacks in a promise chain

Question

I'm having difficulty covering the entire promise chain in my unit test coverage. I did find articles that gave me the nearest solution but the challenge is at the last 'then' I need to call three function that does not return a promise.

Below is the example/Sample I tried

async = jest.fn(() => {
  return Promise.resolve('value');
});

async1 = jest.fn(() => {
  return Promise.resolve('value1');
});

async2 = jest.fn(() => {
  return Promise.resolve('Final Value');
});


it('test my scenario', (done) => {
  someChainPromisesMethod()
    .then(data => {
      expect(async1).toBeCalledWith('value');
      expect(async2).toBeCalledWith('value1');
      expect(data).toEqual('Final Value');
      done(); 
  });
});

Below is the function which returns another function with nested 'then' functions. I need help with the test cases to cover them all.

function consolidatedReport(param1, param2){

   const somedata = param1.data;
   const someOtherData = param2.data;

  if(true){ 
     doThisthing(); 
   }

  return promiseChainBegin(somedata, someOtherData)
    .then(response => response && functionOne(somedata, someOtherData)
    .then(response => response && functionTwo(somedata, someOtherData)
    .then(response => response && functionThree(somedata, someOtherData)
    .then(response => response && functionFour(somedata, someOtherData)
    .then(response => {
       if(response) {
           notApromiseFuncOne(somedata)(someOtherData);
           notApromiseFuncTwo(somedata)(someOtherData);
           notApromiseFuncThree(somedata)(someOtherData);
        } else{
           notApromiseFailCase(someOtherData);
        }
    });
}

I'm having difficulty covering the nested then functions.

Answer 1

You'd mock each of functionOne , etc resolved values:

import functionOne from '../path/to/functionOne';
import functionTwo from '../path/to/functionTwo';
import functionThree from '../path/to/functionThree';

jest.mock('../path/to/functionOne');
jest.mock('../path/to/functionTwo');
jest.mock('../path/to/functionThree');

it('test my scenario', () => {
  functionOne.mockResolvedValue('value 1');
  functionTwo.mockResolvedValue('value 2');
  functionTwo.mockResolvedValue('value 3');

  return someChainPromisesMethod()
    .then(data => {
      expect(functionOne).toBeCalledWith('value returned by promise');
      expect(functionTwo).toBeCalledWith('value 1');
      expect(functionThree).toBeCalledWith('value 2');

      expect(data).toEqual('Final Value');
  });
});

This is not exactly your code, but the idea goes like that. You mock the resolved value for each of your functions.