Jest mockable modules w/ original invocation

mock.js

// Mock specific module pre-inclusion, overwriting methods
// w/ stub that behave the same way.
//
// Module should be absolute path as it will be 'required'
// relative to this 'mock' module
function mock_module(module){
  jest.doMock(module, () => {
    const actual = jest.requireActual(module)

    // Stub original behaviour w/ a jest mock
    Object.keys(actual).forEach((k) => {
      const orig = actual[k]
      
      if(typeof orig == 'function')
        actual[k] = jest.fn().mockImplementation(orig);
    })  

    return actual;
  })  
}

module.exports = {
  mock_module
}

module.js

// This is the module that we are mocking w/ member functions that will be stubbed
// In this example it is to be placed in the parent directory of tests/

module.exports = {
  do_something : function(param){
    return 'returned';
  }
}

module.test.js

// Your jest based test

const path = require('path')
const { mock_module } = require('./mock')

describe("module", () => {
  var _module;
  
  beforeEach(function(){
    mock_module(path.normalize(__dirname + '../module'))
    _module = require('../module')
  })
  
  it("invokes do_something", () => {
    expect(_module.do_something(42)).toEqual('returned')
    expect(_module.do_something).toHaveBeenCalledTimes(1)
    expect(_module.do_something.mock.calls[0][0]).toBe(42)
  })
  
  it("stubs methods", () => {
    _module.do_something.mockReturnValue('alternate');
    expect(_module.do_something()).toEqual('altenate');
  });
})