double-0.spec.js

const double = require('./double-0');

describe('double', () => {
  it('should modify array in place mutating ref declared in outer scope', () => {
    const a = [1, 2, 3];
    const b = double(a);
    expect(a).toEqual([2, 4, 6]);
    expect(b).toEqual([2, 4, 6]);
    expect(a).toBe(b);
  });
});