ES2016 Class, Sinon Stub Constructor

Question

I'm trying to stub out a super call with sinon, and es2016 but I'm not having much luck. Any ideas why this isn't working?

Running Node 6.2.2, this might be an issue with its implementation of classes/constructors.

.babelrc file:

{
  "presets": [
    "es2016"
  ],
  "plugins": [
    "transform-es2015-modules-commonjs",
    "transform-async-to-generator"
  ]
}

Test:

import sinon from 'sinon';

class Foo {
  constructor(message) {
    console.log(message)
  }
}

class Bar extends Foo {
  constructor() {
    super('test');
  }
}

describe('Example', () => {
  it('should stub super.constructor call', () => {
    sinon.stub(Foo.prototype, 'constructor');

    new Bar();

    sinon.assert.calledOnce(Foo.prototype.constructor);
  });
});

Result:

test
AssertError: expected constructor to be called once but was called 0 times
    at Object.fail (node_modules\sinon\lib\sinon\assert.js:110:29)
    at failAssertion (node_modules\sinon\lib\sinon\assert.js:69:24)
    at Object.assert.(anonymous function) [as calledOnce] (node_modules\sinon\lib\sinon\assert.js:94:21)
    at Context.it (/test/classtest.spec.js:21:18)

Note: this issue seems to only happen for constructors. I can spy on methods inherited from the parent class without any issues.

Answer 1

You'll need to setPrototypeOf the subClass due to the way JavaScript implements inheritance.

const sinon = require("sinon");

class Foo {
  constructor(message) {
    console.log(message);
  }
}

class Bar extends Foo {
  constructor() {
    super('test');
  }
}

describe('Example', () => {
  it('should stub super.constructor call', () => {
    const stub = sinon.stub().callsFake();
    Object.setPrototypeOf(Bar, stub);

    new Bar();

    sinon.assert.calledOnce(stub);
  });
});