Unit Test Angularjs directive, which contains priv

I have a directive, which should behave differently, depending on how much time passed since it's initialization:

am.directive('showText', () => ({
  restrict: 'E',
  replace: true,
  scope: {
    value: '@'
  },
  controller: ($scope, $timeout) => {
    console.log('timeout triggered');

    $scope.textVisible = false;

    let visibilityCheckTimeout = $timeout(() => {
      if (parseInt($scope.value, 10) < 100) {
        $scope.textVisible = true;
      }
    }, 330);

    // Clear timeout upon directive destruction
    $scope.$on('$destroy', $timeout.cancel(visibilityCheckTimeout));
  },
}));

The problem is, that when I'm trying to test it with Jasmine, I can't seem to find a way to trigger this timeout in any way. Already tried a $timeout.flush() and $timeout.verifyNoPendingTasks() (which actually throws an error, if I'll comment flush call). But it's still not triggering that timeout's callback execution

describe('showText.', () => {
  let $compile;
  let $rootScope;
  let $scope;
  let $timeout;

  const compileElement = (rootScope, value = 0) => {
    $scope = rootScope.$new();
    $scope.value = value;

    const element = $compile(`
      <show-text
        value="value"
      ></show-text>
    `)($scope);

    $scope.$digest();

    return element;
  };

  beforeEach(() => {
    module('app.directives.showText');

    inject((_$compile_, _$rootScope_, _$timeout_) => {
      $compile = _$compile_;
      $rootScope = _$rootScope_;
      $timeout = _$timeout_;
    });
  });

  it(`Process lasts > 0.33s. Should show text.`, () => {
    const VALUE = 30;
    const element = compileElement($rootScope, VALUE);
    const elementContent = element.find('.show-text__content');

    $timeout.flush(1000);

    $timeout.verifyNoPendingTasks();

    $rootScope.$digest();

    expect(element.isolateScope().textVisible).toBeTruthy();
    expect(elementContent.length).toEqual(1);
    expect(elementContent.text().trim()).toBe('Example text');
  });
});

Test fails.

Can't find what am I doing wrong. Any tips on how to properly test such a case?

Thanks.

UPD After some investigation, I've found that in this particular test-case, in compileElement function, value property isn't being evaluated by $compile service. And equals "value". I've used same function already 10th of times, and can't get, why it's not taking a $scope.value's property as it was before.

The reason why this happens is that $timeout.cancel(visibilityCheckTimeout) launches unconditionally and immediately. Instead, it should be

$scope.$on('$destroy', () => $timeout.cancel(visibilityCheckTimeout));

There are things that can be done to improve testability (besides the fact that $timeout works here as one-time scope watcher and asks to be replaced with the one).

$timeout can be successfully spied:

beforeEach(module('app', ($provide) => {
  $provide.decorator('$timeout', ($delegate) => {
    var timeoutSpy = jasmine.createSpy().and.returnValue($delegate);
    angular.extend(timeoutSpy, $delegate);
    spyOn(timeoutSpy, 'cancel').and.callThrough();
    return timeoutSpy;
  });
}));

Private $timeout callback can be exposed to scope.

$scope._visibilityCheckHandler = () => {
  if (parseInt($scope.value, 10) < 100) {
    $scope.textVisible = true;
  }
};
$timeout($scope._visibilityCheckHandler, 330);

This way all of the calls can be spied and get full coverage:

let directiveScope;
...

const element = $compile(`...`)($scope);

directiveScope = element.isolateScope();
spyOn(directiveScope, '_visibilityCheckHandler').and.callThrough();

$scope.$digest();
...

expect($timeout).toHaveBeenCalledWith(directiveScope._visibilityCheckHandler, 330);
expect($timeout.cancel).not.toHaveBeenCalled();

In this case here's no need to have separate specs for '>= 0.33s' and '< 0.33s' with flush delay argument, $timeout's inner work was already tested in Angular specs. Also, callback logic can be tested separately from $timeout spec.