Angular basic promise test.js

it('should simulate promise', inject(function($q, $rootScope) {
    var deferred = $q.defer();
    var promise = deferred.promise;
    var resolvedValue;

    promise.then(function(value) { resolvedValue = value; });
    expect(resolvedValue).toBeUndefined();

    // Simulate resolving of promise
    deferred.resolve(123);
    // Note that the 'then' function does not get called synchronously.
    // This is because we want the promise API to always be async, whether or not
    // it got called synchronously or asynchronously.
    expect(resolvedValue).toBeUndefined();

    // Propagate promise resolution to 'then' functions using $apply().
    $rootScope.$apply();
    expect(resolvedValue).toEqual(123);
}));