const expect = require('expect'); const getDaysDiffBetweenDates = require('./getDaysDiffBetweenDates.js'); test('getDaysDiffBetweenDates is a Function', () => { expect(getDaysDiffBetweenDates).toBeInstanceOf(Function); }); test('Returns the difference in days between two dates', () => { expect(getDaysDiffBetweenDates(new Date('2017-12-13'), new Date('2017-12-22'))).toBe(9); });