text: const expect = require('chai').expect;
  const letterCombinations =
      require('../../../main/algorithm/medium/LetterCombinationsOfAPhoneNumber');
  
  describe('Letter Combinations of a Phone Number', function() {
      it('"23" should return ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"]', function() {
          expect(letterCombinations('23')).to.deep.equal(['ad', 'ae', 'af', 'bd', 'be', 'bf', 'cd', 'ce', 'cf']);
      });
  });