javascript - 在单元测试中观察 AngularJS 属性时，newValue 始终等于 oldValue

Question

我有一个 Controller ，它只是监视“名称”属性并在发生任何更改时打印其新值和旧值。

function Ctrl($scope) {
    $scope.$watch('name', function(newValue, oldValue) {
        console.log('newValue: ' + newValue + ', oldValue: '+ oldValue);
        if (newValue !== oldValue) {
            //...
        }
    }
});

然后我想用 Jasmine 对其进行单元测试:

var rootScope, scope, ctrl;
beforeEach(inject(function ($rootScope, $controller) {
    rootScope = $rootScope;
    scope = $rootScope.$new();
    ctrl = $controller('Ctrl', { $scope: scope });
}));

it('should have different old and new values if I set a new name', function() {
    rootScope.name = 'some new name';
    rootScope.$apply();

    //expect the behaviors happen for newValue !== oldValue
});

然后我希望控制台记录一条消息，指示 newValue 不等于 oldValue，但是我总是得到 newValue === oldValue。为什么旧值丢失了？

Answer 1

我认为，这就是行为。当我们第一次调用 Controller 时，旧值等于新值，因此什么也没有发生。一般在这种情况下我们可以这样写:

if(oldValue === newValue){return;}

我们也可以这样写$watch:

$scope.$watch('name', function () {
    // ....
  });

并且仅当 name 更改时才会调用:

演示 1 Plunker

我不是 Unitest Guru，无论如何尝试一下这个流程:

Controller

angular.module('plunker').controller('MyCtrl', function($scope) {

 $scope.watchFunctionCounter= 0;

  $scope.$watch(function () {
    return $scope.name;
},
function (newValue, oldValue) {
    console.log('newValue: ' + newValue + ', oldValue: '+ oldValue);
        if (newValue !== oldValue) {
            $scope.watchFunctionCounter++;
        }
}, true);
});

Unitest

describe('Directive: maybeLink', function() {
 var scope, ctrl;

  beforeEach(function() {
    module('plunker');

    inject(function($rootScope, $controller) {
      scope = $rootScope.$new();
      ctrl = $controller('MyCtrl', {$scope: scope});
    });
  });

  afterEach(function() {
        controller = null;
    });

        it('should have different old and new values if I set a new name', function() {
           scope.name = 'some new name';
           scope.$digest();

          expect(scope.watchFunctionCounter).toBe(0); 
         // on this strage the name is undefined, therefore we stay out of "if" statemant

           scope.name = 'diff name';
           scope.$digest();

          expect(scope.watchFunctionCounter).toBe(1);
     });
});

演示 2 Plunker