Asynchronous Unit Testing - Have your Test Case inherit from it to utilize it - ref: https://gist.github.com/andrewroycarter/2254570 License: BSD 3-Clause

CBAsyncTestCase.h

//
//  CBAsyncTestCase.h
//
//  Created by Christopher Bess
//

#import <SenTestingKit/SenTestingKit.h>

@interface CBAsyncTestCase : SenTestCase

/**
 * Begins the async operation watch.
 * @discussion Call before async operation begins.
 */
- (void)beginAsyncOperation;

/**
 * Finishes the async operation watch, call to complete operation and prevent timeout.
 */
- (void)finishedAsyncOperation;

/**
 * Waits for the async operation to finish or returns as a timeout.
 * @return YES if the async operation timeout interval is exceeded, NO if the
 * async operation finished.
 */
- (BOOL)waitForAsyncOperationOrTimeoutWithInterval:(NSTimeInterval)interval;
- (BOOL)waitForAsyncOperationOrTimeoutWithDefaultInterval; // timeout: 10secs

- (void)assertAsyncOperationTimeout; // uses default interval

@end

CBAsyncTestCase.m

//
//  CBAsyncTestCase.m
//
//  Created by Christopher Bess
//  

#import "CBAsyncTestCase.h"

@implementation CBAsyncTestCase {
    dispatch_semaphore_t _networkSemaphore;
    BOOL _didTimeout;
}

- (void)beginAsyncOperation
{
    _didTimeout = NO;
    _networkSemaphore = dispatch_semaphore_create(0);
}

- (void)finishedAsyncOperation
{
    _didTimeout = NO;
    [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(timeoutAsyncOperation) object:nil];
    
    dispatch_semaphore_signal(_networkSemaphore);
}

- (BOOL)waitForAsyncOperationOrTimeoutWithDefaultInterval
{
    return [self waitForAsyncOperationOrTimeoutWithInterval:10];
}

- (BOOL)waitForAsyncOperationOrTimeoutWithInterval:(NSTimeInterval)interval
{
    [self performSelector:@selector(timeoutAsyncOperation) withObject:nil afterDelay:interval];
    
    // wait for the semaphore to be signaled (triggered)
    while (dispatch_semaphore_wait(_networkSemaphore, DISPATCH_TIME_NOW))
    {
        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate dateWithTimeIntervalSinceNow:10]];
    }
    
    return _didTimeout;
}

- (void)timeoutAsyncOperation
{
    _didTimeout = YES;
    dispatch_semaphore_signal(_networkSemaphore);
    //STFail(@"Async operation timed out."); // auto-fail
}

- (void)assertAsyncOperationTimeout
{
    STAssertFalse([self waitForAsyncOperationOrTimeoutWithDefaultInterval], @"timed out");
}

@end

MyTestCase.m

// This Test Case class uses CBAsyncTestCase as the base class

- (void)testNetworkStuff
{
    [self beginAsyncOperation];

    NSString *identifier = @"777";
    [_networkManager fetchStuffWithID:identifier completion:^(NSArray *results, NSError *error) {

        STAssertNil(error, @"error occurred: %@", error);
        STAssertTrue(results.count, @"no results");
        
        [self finishedAsyncOperation];
    }];
    
    // waits for async operation or timeout and fail assertion
    [self assertAsyncOperationTimeout];
}

Moved to: https://github.com/cbess/CBAsyncTestCase