Ошибка в модульном тесте Kiwi

Question

Я изучаю юнит-тест. Я собираюсь использовать Kiwi Framework.I написал простой тестовый код с использованием удара киви:

#import <Kiwi/Kiwi.h>

SPEC_BEGIN(SimpleStringSpec)

describe(@"SimpleString", ^{
    context(@"when assigned to 'Hello world'", ^{
        NSString *greeting = @"Hello world";
        it(@"should exist", ^{
            [[greeting shouldNot] beNil];
        });

        it(@"should equal to 'Hello world'", ^{
            [[greeting should] equal:@"Hello world"];
        });
    });
});

SPEC_END

При тестировании кода Project завершится с ошибкой:

12:26:50.842 XCTest_Demo[8053:93923]    _XCT_testBundleReadyWithProtocolVersion:minimumVersion: reply received
12:26:50.852 XCTest_Demo[8053:93923] _IDE_startExecutingTestPlanWithProtocolVersion:16
2016-05-25 12:26:50.856 XCTest_Demo[8053:93891] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '+[NSInvocation    _invocationWithMethodSignature:frame:]: method signature argument cannot be nil'
*** First throw call stack:
(
0   CoreFoundation                      0x0000000109a4dd85 __exceptionPreprocess + 165
1   libobjc.A.dylib                     0x0000000107949deb objc_exception_throw + 48
2   CoreFoundation                      0x000000010990d71d +[NSInvocation _invocationWithMethodSignature:frame:] + 333
3   XCTest                              0x0000000111b38ea9 -[XCTestCase initWithSelector:] + 167
4   XCTest                              0x0000000111b38f08 +[XCTestCase testCaseWithSelector:] + 43
5   XCTest                              0x0000000111b374cb +[XCTestSuite testSuiteForTestCaseWithName:] + 344
6   XCTest                              0x0000000111b38181 -[XCTestSuite _initWithTestConfiguration:] + 508
7   XCTest                              0x0000000111b38674 +[XCTestSuite testSuiteForTestConfiguration:] + 50
8   XCTest                              0x0000000111b24979 -[XCTestDriver _runSuite] + 233
9   XCTest                              0x0000000111b257d1 -[XCTestDriver _checkForTestManager] + 259
10  XCTest                              0x0000000111b6fa9a _XCTestMain + 628
11  CoreFoundation                      0x00000001099732ec __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 12
12  CoreFoundation                      0x0000000109968f75 __CFRunLoopDoBlocks + 341
13  CoreFoundation                      0x00000001099686d2 __CFRunLoopRun + 850
14  CoreFoundation                      0x00000001099680f8 CFRunLoopRunSpecific + 488
15  GraphicsServices                    0x000000010b74bad2 GSEventRunModal + 161
16  UIKit                               0x0000000107daef09 UIApplicationMain + 171
17  XCTest_Demo                         0x0000000107456c5f main + 111
18  libdyld.dylib                       0x000000010a6a592d start + 1
19  ???                                 0x0000000000000005 0x0 + 5
)
libc++abi.dylib: terminating with uncaught exception of type NSException

В чем дело?