double-1.spec.js

const double = require('./double-1');

describe('double', () => {
  it('should create new array without mutating ref declared in outer scope', () => {
    const a = [1, 2, 3];
    const b = double(a)
    expect(a).toEqual([1, 2, 3]);
    expect(b).toEqual([2, 4, 6]);
    expect(a).not.toBe(b);
  });
});