测试属性的angularjs指令

Question

我有以下指令，它工作得很好，现在我需要对它进行单元测试，

(() => {
  angular
    .module('app.utilities')
    .directive('allowPattern', allowPatternDirective);

  function allowPatternDirective () {
    return {
      restrict: 'A',
      compile () {
        return (scope, element, attrs) => {
          element.bind('keypress', (event) => {
            const keyCode = event.which || event.keyCode; // get the keyCode pressed from the event.
            const keyCodeChar = String.fromCharCode(keyCode); // determine the char from the keyCode.
            // keyCode char does not match the allowed Regex Pattern, then don't allow the input into the field.
            if (!keyCodeChar.match(new RegExp(attrs.allowPattern, 'i'))) {
              event.preventDefault();
              return false;
            }
            return true;
          });
        };
      },
    };
  }
})();

下面是我正在运行的单元测试，它失败了，

ngDescribe({
  name: 'allow-pattern',
  modules: ['app.utilities'],
  inject: ['$compile'],
  tests (deps) {
    let scope;
    let element;
    function compileDirective () {
      scope = deps.$rootScope.$new();
      element = deps.$compile('<input allow-pattern="[0-9]">')(scope);
      scope.$digest();
      return element;
    }
    function triggerhandler (eventCode) {
      element.triggerHandler({ type: 'keypress', which: eventCode });
    }
    it.only('sets value if it matches the pattern', () => {
      compileDirective();
      triggerhandler(57); // keycode for 5
      scope.$digest();
      console.log(element.val());
    });
  },
});

现在，每当我运行这个测试时，我希望element.val()的值应该是5，但它返回的却是空字符串。我不能理解哪里出了问题。谁能指出问题所在？

我正在使用因果报应和幻影。

提前谢谢。