Started waiting for the notifications locally before asserting side effects

[gaaclarke]

fixes flutter/flutter#79011

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• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt. See testing the engine for instructions on
  writing and running engine tests.
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[jmagman]

LGTM!

[fluttergithubbot]

This pull request is not suitable for automatic merging in its current state.

• The status or check suite Mac iOS Engine has failed. Please fix the issues identified (or deflake) before re-applying this label.

[jmagman]

Guess that didn't work...

FlutterViewController.mm:613: error: -[FlutterPluginAppLifeCycleDelegateTest testWillResignActive] : failed: caught "NSInternalInconsistencyException", 
"** Cannot use mock object OCClassMockObject(FlutterEngine) at 0x6000002144b0. This error usually occurs when a mock object is used after stopMocking has been called on it. In most cases it is not necessary to call stopMocking. If you know you have to, please make sure that the mock object is not used afterwards."

https://logs.chromium.org/logs/flutter/buildbucket/cr-buildbucket.appspot.com/8851835021381396112/+/steps/Host_Tests_for_ios_debug_sim/0/stdout

[jmagman]

It's failing on the -[NSNotificationCenterpostNotificationName::] line before it even gets here.

	0   CoreFoundation                      0x000000010e14de6e __exceptionPreprocess + 350
	1   libobjc.A.dylib                     0x000000010d5b19b2 objc_exception_throw + 48
	2   CoreFoundation                      0x000000010e14dcac +[NSException raise:format:] + 188
	3   libocmock_shared.dylib              0x0000000126ec2448 -[OCMockObject handleInvocation:] + 39
	4   libocmock_shared.dylib              0x0000000126ec2327 -[OCMockObject forwardInvocation:] + 30
	5   CoreFoundation                      0x000000010e152616 ___forwarding___ + 838
	6   CoreFoundation                      0x000000010e154c58 __forwarding_prep_1___ + 120
	7   libios_test_flutter.dylib           0x0000000126f4aa5d -[FlutterViewController surfaceUpdated:] + 187
	8   libios_test_flutter.dylib           0x0000000126f4b59d -[FlutterViewController applicationWillResignActive:] + 46
	9   CoreFoundation                      0x000000010e078d2c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 12
	10  CoreFoundation                      0x000000010e0781a5 _CFXRegistrationPost1 + 421
	11  CoreFoundation                      0x000000010e077f11 ___CFXNotificationPost_block_invoke + 193
	12  CoreFoundation                      0x000000010e175473 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1795
	13  CoreFoundation                      0x000000010e077866 _CFXNotificationPost + 950
	14  Foundation                          0x000000010cff426b -[NSNotificationCenter postNotificationName:object:userInfo:] + 59
	15  libios_test_flutter.dylib           0x0000000126ef9932 -[FlutterPluginAppLifeCycleDelegateTest testWillResignActive] + 200

Cannot use mock object OCClassMockObject(FlutterEngine)
Where even is that FlutterEngine mock even coming from? I see a OCMClassMock([FlutterEngine class]) set up in FlutterTextInputPluginTest and FlutterViewControllerTest (the latter is my guess) but not this test. Maybe the view controllers in those tests are still alive after -tearDown and are trying to notify their dead engines? Is there a retain cycle somewhere?

[gaaclarke]

Yea, it's a leak from another test somewhere. I'm guessing there is a stray mock engine that is getting talked to when the notification is sent (since the flutterengine also listens to those notifications). I gotta add a stopMocking somewhere, or maybe see where it isn't removing itself as an observer when it should be. The retain cycle might be created by not calling stopMocking and not necessarily a problem in the code. I'll see what I can find.

[gaaclarke]

Found it, it was the partial mock in testCallsNotifyLowMemory. I added a few extra stopMocking calls for FlutterEngines.

[jmagman]

I'm not sure that's the problem, the error is complaining that stopMocking had already been called on the engine, but a FlutterViewController is trying to tell it about surfaceUpdated.

Cannot use mock object OCClassMockObject(FlutterEngine) at 0x6000002144b0. This error usually occurs when a mock object is used after stopMocking has been called on it.

The only two OCMClassMock([FlutterEngine class]) I see are in FlutterTextInputPluginTest and FlutterViewControllerTest. Are the FlutterViewControllers in FlutterViewControllerTest dealloced after -tearDown? It doesn't look like it should be since the self.mockEngine is nil'd out in -tearDown which should break the retain cycle, but maybe I'm missing something.

  FlutterViewController* viewControllerB =
      [[FlutterViewController alloc] initWithEngine:self.mockEngine nibName:nil bundle:nil];
...
OCMStub([self.mockEngine viewController]).andReturn(viewControllerB);

Might be easiest to check if the memory graph contains any FlutterViewControllers before FlutterPluginAppLifeCycleDelegateTest starts.

[gaaclarke]

I've seen this problem because the mock object can cause retains on objects that aren't apparent, stopMocking flushes them out. That was the thesis behind the change. I saw those other tests that deleting the engine, that may be the problem. Let me try that out.

[gaaclarke]

This is the fix to the problem we had with the engine.