Angular test using $httpBackend fails with "400 thrown" error - angularjs

Question

For hours I've been trying to test my NewPostController with $httpBackend. The problem is whenever I set non-2xx status code in the response, the test fails.
NewPostController has the following method:
$scope.submit = function () {
var newPost = $scope.newPost;
PostService.insertPost(newPost).then(function (post) {
$location.path("/my-posts");
}, function (status) {
$scope.form.$setPristine();
$scope.error = status;
});
};
I have a problem testing the failure path:
it(...) {
...
$scope.post.text = "";
$httpBackend.expectPOST("/create-post", {"post":$scope.post}).respond(400);
$scope.submit();
$httpBackend.flush();
expect($scope.error).toBeDefined();
$scope.post.text = "This is a valid text.";
$httpBackend.expectPOST("/create-post", {"post": $scope.post}).respond(200);
$scope.submit();
$httpBackend.flush();
expect($location.path()).toBe("/my-posts");
});
The test fails with a message "400 thrown" (no callstack). I tried to change the order of subtests, use whenPOST instead of expectPOST and combine the methods as they do in Angular docs (https://docs.angularjs.org/api/ngMock/service/$httpBackend) but without success.
Please help.
EDIT:
Now when I look at PostService, it makes sense where the "400 thrown" comes from but I expected the error to be handled by angular. I threw it because of the section "Handling problems in nested service calls" of this article. It is supposed to be a shorter version of deferred.resolve/reject mechanism.
this.insertPost = function (newPost) {
return $http({
method: "post",
url: "/create-post",
data: {
post: newPost
}
}).then(function (res) {
return (res.data);
}, function (res) {
throw res.status;
});
};

Answer 1

This is indeed strange, and is perhaps something the angular team didn't consider.
When a promise is rejected by throwing (as you're doing), the angular $exceptionHandler service is called with the thrown exception. By default, this service just logs the exception in the browser console.
But when using ngMocks, this service is replaced by a mock implementation that can either log or rethrow the exception. The default mode is to rethrow, in order to make a test fail when an exception is thrown.
My advice would be to avoid using throw to simply reject a promise, and thus replace
function (res) {
throw res.status;
}
by
function (res) {
return $q.reject(res.status);
}
But if you really want to keep using throw, you can also configure the mock exceptionHandler to log instead of rethrowing:
beforeEach(module(function($exceptionHandlerProvider) {
$exceptionHandlerProvider.mode('log');
}));