An example of a spy and stub

spy_and_stub.js

import expect from 'expect';
import sinon from 'sinon';
import fetch from 'isomorphic-fetch';

describe.only('Sinon samples', () => {
	describe('spy', () => {

		let spy;
		before(() => {
			let add = (...args) => args.reduce((a, b) => a + b);
			spy = sinon.spy(add);
		})
		
		it('Should add two numbers', () => {
			spy(2, 3);
			expect(spy.withArgs(2, 3).calledOnce).toBe(true);
			expect(spy.returned(5)).toBe(true);
		});

	});

	describe('stub', () => {

		let stub, object, expected;
		before(() => {
			object = {};
			object.method = () => {
				return fetch('https://jsonplaceholder.typicode.com/users')
					.then((response) => response.json())
					.then((data) => data);
			}
			stub = sinon.stub(object, 'method');
			expected = [{id: 1, name: 'Matt'}];
			stub.returns(expected);
		});
		
		it('Should return the expected data', (done) => {
			Promise.resolve(object.method()).then((actual) => {
				expect(actual).toEqual(expected);
				done();
			});
		});

	});
});