Sinon Class Constructor

Question

I have an Animal class as follows

Animal.js

export default class Animal {
  constructor(type) {
    this.type = type
  }
  getAnimalSound(animal) {
    if (animal && animal.type == 'dog') return 'woof'
    if (animal && animal.type == 'cat') return 'meow'
  }
}

I make a zoo module which has a method for getAnimalSound() as follows

zoo.js

import Animal from './Animal'

export default function getAnimalSound(type) {
  let animal = new Animal(type)
  let animalSound = animal.getAnimalSound(animal)
  return animalSound
}

Now how do i make unit testing for zoo module?

zoo.test.js

import sinon from 'sinon'

import Animal from './Animal'
import getAnimalSound from './zoo'

let animalStub = sinon.createStubInstance(Animal)
let a = animalStub.getAnimalSound.returns('woof')
let sound = getAnimalSound('cat')
console.log(sound)

So the problem is that the 'new' has no effect by the way i have stubbed in test.js Can i achieve this?

Regards Bobu P

Answer 1

You could use Link Seams to mock your ./animal.js module and Animal class.

E.g.

animal.ts:

export default class Animal {
  type: any;
  constructor(type) {
    this.type = type;
  }
  getAnimalSound(animal) {
    if (animal && animal.type == 'dog') return 'woof';
    if (animal && animal.type == 'cat') return 'meow';
  }
}

zoo.ts:

import Animal from './animal';

export default function getAnimalSound(type) {
  let animal = new Animal(type);
  let animalSound = animal.getAnimalSound(animal);
  return animalSound;
}

zoo.test.ts:

import sinon from 'sinon';
import proxyquire from 'proxyquire';
import { expect } from 'chai';

describe('61716637', () => {
  it('should pass', () => {
    const animalInstanceStub = {
      getAnimalSound: sinon.stub().returns('stubbed value'),
    };
    const AnimalStub = sinon.stub().returns(animalInstanceStub);
    const getAnimalSound = proxyquire('./zoo', {
      './animal': { default: AnimalStub },
    }).default;
    const actual = getAnimalSound('bird');
    expect(actual).to.be.equal('stubbed value');
    sinon.assert.calledWith(AnimalStub, 'bird');
    sinon.assert.calledWith(animalInstanceStub.getAnimalSound, animalInstanceStub);
  });
});

unit test results with coverage report:

  61716637
    ✓ should pass (2242ms)


  1 passing (2s)

-----------|---------|----------|---------|---------|-------------------
File       | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
-----------|---------|----------|---------|---------|-------------------
All files  |   54.55 |        0 |   33.33 |   66.67 |                   
 animal.ts |   16.67 |        0 |       0 |      25 | 4-8               
 zoo.ts    |     100 |      100 |     100 |     100 |                   
-----------|---------|----------|---------|---------|-------------------