XCTest KVO exception: "Cannot remove an observer <_XCKVOExpectation ..."
XCTest KVO exception: "Cannot remove an observer <_XCKVOExpectation ..."
- Subject: XCTest KVO exception: "Cannot remove an observer <_XCKVOExpectation ..."
- From: Jens Alfke <email@hidden>
- Date: Mon, 17 Aug 2015 13:53:45 -0700
I’ve been using the very handy “expectation” API in XCTestCase, for testing asynchronous operations. But one particular test is occasionally failing in our Xcode bot, never for me, with a weird exception. It looks like the implementation of -keyValueObservingExpectationForObject:… isn’t handling KVO registration properly:
Assertion: failed: caught "NSRangeException", "Cannot remove an observer <_XCKVOExpectation 0x1056a00c0> for the key path "fractionCompleted" from <NSProgress 0x10a01ae90> because it is not registered as an observer."
(
0 CoreFoundation 0x00007fff8ab8403c __exceptionPreprocess + 172
1 libobjc.A.dylib 0x00007fff9249c76e objc_exception_throw + 43
2 CoreFoundation 0x00007fff8ab83eed +[NSException raise:format:] + 205
3 Foundation 0x00007fff90f5a896 -[NSObject(NSKeyValueObserverRegistration) _removeObserver:forProperty:] + 604
4 Foundation 0x00007fff90f5a5d9 -[NSObject(NSKeyValueObserverRegistration) removeObserver:forKeyPath:] + 114
5 XCTest 0x0000000100099d57 -[_XCKVOExpectation _safelyUnregister] + 96
6 XCTest 0x000000010008eae2 -[_XCTestCaseImplementation resetExpectations] + 231
7 CBL Mac Unit Tests 0x0000000104bf2f5c -[Replication_Tests test20_LazyPullAttachments] + 10268
8 CoreFoundation 0x00007fff8aa5b7bc __invoking___ + 140
9 CoreFoundation 0x00007fff8aa5b612 -[NSInvocation invoke] + 290
10 XCTest 0x000000010008b9fc -[XCTestCase invokeTest] + 253
11 CBL Mac Unit Tests 0x0000000104a78b37 -[CBLTestCaseWithDB invokeTest] + 119
12 CBL Mac Unit Tests 0x0000000104ba7275 -[Replication_Tests invokeTest] + 69
13 XCTest 0x000000010008bbfb -[XCTestCase performTest:] + 150
…
I’m not sure what to do about this since I own neither the code that does the observing nor the class being observed. I’ll probably file a bug against Xcode, but I’m wondering if anyone else has run into this exception?
—Jens
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