text: 'use strict';
  
  module.exports = function () {
      var importantPrivateCounterVariable = 0;
  
      return {
          sum: function (a, b) {
              importantPrivateCounterVariable++;
              return a + b;
          },
  
          getCallCount: function () {
              return importantPrivateCounterVariable;
          }
      }
  };