Another way to test global functions

double-console.spec.ts

import { expect } from 'chai';
import { match, stub } from 'sinon';
import { doubleConsole } from '../src/double-console';

describe.only('doubleConsole()', () => {
	let callbackSetImmediate: any;
	let callbackSetTimeout: any;

	beforeEach(() => {
		stub(global, 'setImmediate').callsFake((x) => {
			callbackSetImmediate = x;
			return undefined as any;
		});
		stub(global, 'setTimeout').callsFake((x) => {
			callbackSetTimeout = x;
			return undefined as any;
		});
		stub(console, 'log');
	});

	it('should call console.log twice with a 100 ms interval', () => {
		doubleConsole();

		expect(console.log).calledOnceWithExactly('Now you see me');
		expect(global.setTimeout).to.have.been.calledOnceWithExactly(match.func, 100);
		expect(global.setImmediate).to.have.been.calledOnceWithExactly(match.func);
		callbackSetImmediate();
		expect(console.log).calledTwice.calledWithExactly('Now still');
		callbackSetTimeout();
		expect(console.log).calledThrice.calledWithExactly("Now you don't");
	});
})