如何用Sinon存根扩展ES6类的构造函数

Question

So I'm having a few issues with stubbing constructors, and more-so inherited classes constructors... I'll start with some sample code snippets:

Parent.js

module.exports = class Parent {
  constructor (){
    // code I don't want to run during tests
  }
}

MyClass.js

let Parent = require('path/to/Parent');

module.exports = class MyClass extends Parent {
  // no overridden constructor
}

Mocha Test

let MyClass = require('path/to/MyClass')

...

test('test1', (done) => {
  // I want to stub the MyClass/Parent constructor before creating a new instance
  // of MyClass so that the constructor code in Parent doesn't run

  let myClass = new MyClass();
  // assertions 'n' stuff
  return done();
});

...

I've tried a few things already but always find that the code in Parent constructor gets run regardless of what I do... I have a feeling it might have something to do with MyClass requiring Parent before a get a chance to stub it.

I've also tried using rewire to replace the variable in MyClass, but not joy there either; eg

let MyClass = rewire('path/to/MyClass');
MyClass.__set__('Parent', sinon.stub());

Any suggestions/help on how I might achieve what I'm trying to do here?

Answer 1

I haven't used rewire so I'm not sure why it doesn't work but stubbing the parent constructor would work fine using proxyquire :

const MockParent = sinon.stub()
const MyClass = proxyquire('../../some/path', {
  './Parent': MockParent
})

Answer 2

module.exports = class MyClass extends Parent {
  // no overridden constructor
}

Be equal to:

module.exports = class MyClass extends Parent {
  constructor (...args) {
     super(...args) // be equal to Parent.call(this, ...args)
  }
}

So, the processes are new MyClass() -> MyClass constructor() -> Parent.call() -> Parent constructor()