exports.assertion = function(selector) {
  this.selector = selector;
  this.message = 'Testing if element <' + selector + '> has no descendents.';
  this.expected = true;

  this.pass = function(value) {
    return value && (value.length === 0);
  };

  this.value = function(result) {
    return result && result.value;
  };

  this.command = function(callback) {
    var self = this;
    this.api.elements('css selector', this.selector, function(result) {
      if (result.status === 0 && result.value.length > 0) {
        this.elementIdElements(result.value[0].ELEMENT, 'css selector', '*', function(res) {
          callback(res);
        });
      } else {
        self.message += ' No elements were returned for selector: ' + self.selector;
        callback(false);
      }
    });

    return this;
  };
};