const expect = require('expect'); const differenceWith = require('./differenceWith.js'); test('differenceWith is a Function', () => { expect(differenceWith).toBeInstanceOf(Function); }); test('Filters out all values from an array', () => { expect(differenceWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0], (a, b) => Math.round(a) === Math.round(b))).toEqual([1, 1.2]); });