Example of how to mock a class constructor

get-instance.spec.ts

import * as classToMock from '../src/my-class';
import { getInstance } from '../src/get-instance';
import { stub } from 'sinon';

describe('getInstance()', () => {
	const mockedInstance = {
		info: 'MyClass instance',
	};

	beforeEach(() => {
		stub(classToMock, 'MyClass').returns(mockedInstance);
	});

	it('should return MyClass instance properly created', () => {
    		const result = getInstance();

		expect(classToMock.MyClass).to.have.been.calledOnceExactlyWith(123);
		expect(result).to.be.eq(mockedInstance);
	});
});