text: (function(exports){
    function TenGreenBottles(num){
      if(num < 0) {
          throw new Error('number needs to be greater than 0');
        }
      this.num = num
    }
  
    TenGreenBottles.prototype.sing = function(){
      var lyrics = []
  
      for(counter = this.num ; counter > 0; counter--){
        lyrics.push(this.verseLyrics(counter))
      }
      return lyrics.join('\n')
    }
  
    TenGreenBottles.prototype.verseLyrics =  function(num){
      return [_firstSecondLine(num), _thirdLine(), _lastLine(num)].join('\n');
    }
  
    function _firstSecondLine(num){
      var word;
      num == 1 ? word = 'bottle' : word = 'bottles'
      var line = `${numberToWords.toWords(num).capitalize()} green ${word} sitting on the wall,`;
      return [line, line].join('\n')
    }
  
    function _thirdLine(){
      return 'And if one green bottle should accidentally fall,'
    }
  
    function _lastLine(num){
      var word;
      num - 1 == 1 ? word = 'bottle' : word = 'bottles'
      return `There’ll be ${numberToWords.toWords(num - 1)} green ${word} sitting on the wall.\n`
    }
  
    String.prototype.capitalize = function() {
        return this.charAt(0).toUpperCase() + this.slice(1);
    }
  
    exports.TenGreenBottles = TenGreenBottles;
  
  })(this)
  