code: function _getIdentifier(data) {
          let identifier;
          if (typeof data === 'string') { // name of the mock
              identifier = data;
          } else if (data.name) { // the data containing the name of the mock
              identifier = data.name;
          } else {
              identifier = data.expression + '$$' + data.method;
          }
          return identifier;
      }
docs: Gets the identifier from the provided data object.
  @param data The data object.
  @return {string} identifier The identifier.
  @private