iOS Test crashes with waitForExpectationsWithTimeout

Question

Tests randomly crashes with waitForExpectation, always if I fulfill expectation in dispatch_after.

It happens both in objective-c and swift.

Totally randomly, sometimes it works sometimes not. Does anyone have any idea? ( I am running it using CMD+U on MacMini, but I also tried with MBP Retina, same results)

Example code:

func testBarcodeNotFound() {
        let exp = self.expectationWithDescription("store loading")
        OHHTTPStubs.stubRequestsPassingTest({ (request:NSURLRequest!) -> Bool in
            if request.URL.absoluteString == nil {
                return false
            }
            return request.URL.absoluteString!.hasSuffix("/products/barcode/1422/")
            }, withStubResponse: { (request:NSURLRequest!) -> OHHTTPStubsResponse! in
                let data = "".dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: true)
                return OHHTTPStubsResponse(data: data, statusCode: 404, headers: ["Content-Type":"application/json"])

        })
        self.productsVC.scanningVC.successScan("1422", "EAN13")
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, Int64(0.5 * Double(NSEC_PER_SEC))), dispatch_get_main_queue()) { () -> Void in
            exp.fulfill()
        }

        self.waitForExpectationsWithTimeout(1, handler: nil)

        XCTAssertTrue(self.delegateForProductsVC.barcodeNotFoundCalled)

    }

And backtrace

(lldb) bt
* thread #1: tid = 0x27e405, 0x06461ab0 libdispatch.dylib`_dispatch_semaphore_dispose + 92, queue = 'com.apple.main-thread', stop reason = EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
    frame #0: 0x06461ab0 libdispatch.dylib`_dispatch_semaphore_dispose + 92
    frame #1: 0x06463578 libdispatch.dylib`_dispatch_dispose + 43
    frame #2: 0x064759e1 libdispatch.dylib`_os_object_dispose + 33
    frame #3: 0x06475cb1 libdispatch.dylib`-[OS_dispatch_object _xref_dispose] + 58
    frame #4: 0x064759bb libdispatch.dylib`_os_object_xref_dispose + 33
    frame #5: 0x05759eb1 libobjc.A.dylib`objc_release + 65
    frame #6: 0x2011949d XCTest`__destroy_helper_block_95 + 29
    frame #7: 0x064e4793 libsystem_sim_blocks.dylib`_Block_release + 211
    frame #8: 0x0647603f libdispatch.dylib`_dispatch_client_callout + 14
    frame #9: 0x0645f764 libdispatch.dylib`_dispatch_main_queue_callback_4CF + 470
    frame #10: 0x05af095e CoreFoundation`__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 14
    frame #11: 0x05aaf760 CoreFoundation`__CFRunLoopRun + 2256
    frame #12: 0x05aaebcb CoreFoundation`CFRunLoopRunSpecific + 443
    frame #13: 0x05aae9fb CoreFoundation`CFRunLoopRunInMode + 123
    frame #14: 0x04c2ed98 Foundation`-[NSRunLoop(NSRunLoop) runMode:beforeDate:] + 309
    frame #15: 0x20119a31 XCTest`-[XCTestCase(AsynchronousTesting) waitForExpectationsWithTimeout:handler:] + 1192
  * frame #16: 0x1055be0b SomeAppNative`SomeApp.ProductsDelegatesViewControllerTest.testBarcodeNotFound (self=0x7b0dbdf0)() -> () + 5595 at ProductsDelegatesViewControllerTest.swift:108
    frame #17: 0x1055c1a2 SomeAppNative`@objc SomeApp.ProductsDelegatesViewControllerTest.testBarcodeNotFound (SomeApp.ProductsDelegatesViewControllerTest)() -> () + 34 at ProductsDelegatesViewControllerTest.swift:0
    frame #18: 0x05a7976d CoreFoundation`__invoking___ + 29
    frame #19: 0x05a79618 CoreFoundation`-[NSInvocation invoke] + 360
    frame #20: 0x2010897b XCTest`-[XCTestCase invokeTest] + 320
    frame #21: 0x20108bb9 XCTest`-[XCTestCase performTest:] + 184
    frame #22: 0x20114162 XCTest`-[XCTest run] + 314
    frame #23: 0x20107598 XCTest`-[XCTestSuite performTest:] + 406
    frame #24: 0x20114162 XCTest`-[XCTest run] + 314
    frame #25: 0x20107598 XCTest`-[XCTestSuite performTest:] + 406
    frame #26: 0x20114162 XCTest`-[XCTest run] + 314
    frame #27: 0x20107598 XCTest`-[XCTestSuite performTest:] + 406
    frame #28: 0x20114162 XCTest`-[XCTest run] + 314
    frame #29: 0x20103de2 XCTest`__25-[XCTestDriver _runSuite]_block_invoke + 61
    frame #30: 0x20110c82 XCTest`-[XCTestObservationCenter _observeTestExecutionForBlock:] + 184
    frame #31: 0x20103d06 XCTest`-[XCTestDriver _runSuite] + 285
    frame #32: 0x20104951 XCTest`-[XCTestDriver _checkForTestManager] + 272
    frame #33: 0x20104c6b XCTest`-[XCTestDriver runTestSuite:completionHandler:] + 378
    frame #34: 0x2011775c XCTest`+[XCTestProbe runTests:] + 216
    frame #35: 0x04c2ab57 Foundation`__NSFireDelayedPerform + 423
    frame #36: 0x05af08d6 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 22
    frame #37: 0x05af025d CoreFoundation`__CFRunLoopDoTimer + 1309
    frame #38: 0x05aaf6ba CoreFoundation`__CFRunLoopRun + 2090
    frame #39: 0x05aaebcb CoreFoundation`CFRunLoopRunSpecific + 443
    frame #40: 0x05aae9fb CoreFoundation`CFRunLoopRunInMode + 123
    frame #41: 0x0712e24f GraphicsServices`GSEventRunModal + 192
    frame #42: 0x0712e08c GraphicsServices`GSEventRun + 104
    frame #43: 0x034518b6 UIKit`UIApplicationMain + 1526
    frame #44: 0x0053dae5 SomeApp`main(argc=16, argv=0xbff6e4a4) + 213 at main.m:16
    frame #45: 0x0649cac9 libdyld.dylib`start + 1
(lldb) 

Answer 1

I experienced similar issues and it took me three days to figure out.

The documentation of -waitForExpectationsWithTimeout:handler: says:

 * -waitForExpectationsWithTimeout:handler: runs the run loop while handling events until all expectations
 * are fulfilled or the timeout is reached. Clients should not manipulate the run
 * loop while using this API.

Most likely your NSInputStream or NSOutputStream is trying to affect the runloop during waiting, which will cause a crash.