iOS Testing: dispatch_once get called twice. First in App, second in Test. Problems with Observers

Question

I have a singelton class which will be create in the app delegate.

When i run XCTTests then its get create a second time.

+ (instancetype)urlSchemeManager
{
    static dispatch_once_t onceToken;
    static UrlSchemeManager* _sharedInstance;

    dispatch_once(&onceToken, ^{

        _sharedInstance = [UrlSchemeManager new];


    });
    return _sharedInstance;
}

This is resulting in two different instances. This was no problem if i just use it for unit test. But in the integration test, when i register an observer for urlSchmemeManager i get a EXC_BAD_ACCESS, because it was already observed by the rootViewController (in the UI).

In RootViewController:

UrlSchemeManager * schemeManager = [GlobalSpace globalSpace].urlSchemeManager;
[schemeManager addObserver:self forKeyPath:OBSERVER_KEY_URL_SCHEME_MANAGER_CONTENT_MORE options:NSKeyValueObservingOptionNew context:nil];

Does anyone has an idea how i can get around this problem?

`when i register an observer vor urlSchmemeManager i get a EXT_BAD_ACCESS` what vor stands for? — KudoCC, Jan 09 '14 at 08:17
Didn't you mean EXC_BAD_ACCESS? Could you provide more information about this exception (e.g. stack trace) — CouchDeveloper, Jan 09 '14 at 08:39
There can be only two distinct instances of `_sharedInstance` IFF there are two distinct instances of `onceToken`. This may happen for example when you have two bundles which each include the module where `onceToken` is defined and these bundles will be linked to one application by the dynamic linker. — CouchDeveloper, Jan 09 '14 at 08:58
That sounds linke this could be the reason. Do you have an idea how to solve the problme? — Sam, Jan 09 '14 at 14:54
Well, if the problem genuinely is "library A links to library C + library B links to library C + app links to A & B" the solution is to link all the things in the same link pass, or make sure that all the linkage is dynamic. It's hard to say exactly what's going on here based on only what's posted. — ipmcc, Jan 13 '14 at 13:31

score 34 · Accepted Answer · answered Jan 30 '14 at 22:51

34

I had the same problem with dispatch_once being called multiple times when running a test suite. I fixed it by removing the singleton class from the Target Membership of the Test.

Once you've done that make sure that your test target is dependent on your application in "Build Phases" so that the test still knows about the class.

After that, the test should run and the singleton should only be instantiated one time.

answered Jan 30 '14 at 22:51

Mike Sabatini

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This is the correct solution, I was this close to losing my belief in computers about dispatch_once being executed twice .. Thank you! – floriankrueger Feb 19 '14 at 08:06
Great! You saved my day. – Ryan Jun 12 '15 at 05:44
1

Tests are not compiling if singleton file is not included into the Test target giving the "Use of unresolved identifier" error. – Andrey Gordeev May 28 '17 at 06:29

fsaint · Answer 2 · 2015-07-13T13:15:48.220

Mike's answer is correct! Just adding some more info. This is a really tricky issue. Seems to be the case that app target and the test target are compiled separated. In runtime, however, the binary for the tests is injected into the app's space. Because it is usually the compiler's job to detect duplicate symbols, and the compilation process is different, it can happen that you have two instances of a class at runtime. Each instance of the class with it's own set of static variables. This is super weird. Tons of weird behaviors can stem from this. Including the double dispatch_once_t execution.

I faced this problems in my cocoapods clases. All pods in your Podfile are, by default, linked into all targets. As a result you will have duplicate clases at runtime when running XCTest. The solution is to specify your pods per target. In my case, for example. I did:

source 'https://github.com/CocoaPods/Specs.git'
platform :ios, '7.0'

target 'MyApp', :exclusive => true do
    pod 'AFNetworking'
    pod 'ObjectiveRecord', :head
    ...
end

target 'MyApp Tests', :exclusive => true do
  pod 'KIF', '~> 3.0', :configurations => ['Debug']
end

inhibit_all_warnings!

I specifically had issues with the singleton pattern in ObjectiveRecord. Because the core data context manager class was created twice, different sections of my app were not seeing the same data.

Thanks, this was exactly my issue :) ( BTW, I don't think you need the two `:exclusive => true`s too.) — orta, Oct 29 '15 at 11:08
I've solved my issue by excluding my singleton from test target compilation. The problem was that it was marked for compilation for both app and unitTest targets. That was the source of duplicated symbols. — Chugaister, Sep 02 '16 at 12:32

iOS Testing: dispatch_once get called twice. First in App, second in Test. Problems with Observers

2 Answers2