text: const sum = require('./numbers').sum;
  const expect = require('chai').expect;
  
  describe('sum', () => {
      it('should return NaN when test with string', () => {
          const actual = sum('abc');
          expect(actual).to.be.NaN;
      });
  
      it('should return number when test with array of strings', () => {
          const expected = sum(['1', '2']);
          expect(expected).to.equal(3);
      });
  
      it('should return 6 when invoke sum([1, 2, 3])', () => {
          const expected = 6;
          const actual = sum([1, 2, 3]);
          expect(actual).to.equal(expected);
      });
  });