text: import solution from './index';
  
  describe('perm missing elem solution', () => {
    it('standard test cases', () => {
      expect(solution([2, 3, 1, 5])).toEqual(4);
    });
  
    it('custom test cases', () => {
      expect(solution([1, 4, 3, 5])).toEqual(2);
      expect(solution([4, 3, 5, 2])).toEqual(1);
      expect(solution([1])).toEqual(2);
    });
  });
  