title: jest mock implementation is not working with require('')
body: <p>I want to test one JS which is using one 3rd lib to fetch data, so I am using jest mock that implementation. It is working when I call it directly in the test. However, it is not working when it is used in source code.</p>
  
  <p>Here is the code </p>
  
  <pre><code>//Source implementation
  
  var reference = require('./reference');
  
  module.exports = {
    getResult: function() {
      return reference.result();
    }
  };
  
  
  //Test code
  
  jest.dontMock('./foo');
  jest.dontMock('console');
  
  describe('descirbe', function() {
    var foo = require('./foo');
  
    it('should ', function() {
      var reference = require('./reference');
  
      reference.result.mockImplementation(function (a, b, c) {
        return '123'
      });
  
      console.log(foo.getResult()); // undefined
      console.log(reference.result()); // 123
    });
  
  });
  </code></pre>