node.js - Mocha Sinon Change Constructor

Question

During test There is code that should not be executed inside the constructor function. Since I was new to Sinon, I thought I could do with it. I prepared the sample code below for this.

Person.js

class Person {
    constructor() {
        console.log("From constructor");
    }
}

Test library: app.spec.js

const sinon = require('sinon');
const { Person } = require('../Person');

describe('Person', () => {
    it('Test1', () => {
        const costructorSpy = sinon.spy(Person.prototype, 'constructor');
        new Person();
    });
});

But I still see the console message From constructor on the terminal.

question from:https://stackoverflow.com/questions/65641489/mocha-sinon-change-constructor

Answer 1

if you want to replace constructor behaviour replace it with a stub, not a spy. Use sinon's createStubInstance() method for this

const sinon = require('sinon');
const { Person } = require('../Person');

describe('Person', () => {
    it('Test1', () => {
        const replacedConstructor = sinon.createStubInstance(Person).returns();
        new Person();
    });
});

docs for this are written here https://sinonjs.org/releases/v9.2.3/stubs/