Detects object deallocations. Good for testing.

DetectDeallocations.h

// Runs given block. Returns YES if some object of class ‘c’
// was deallocated in the block. Not thread-safe.
BOOL classGetsDeallocated(Class c, void (^block)(void));

// Convenience interface that calls the function above.
// Releases object, returns YES if object was deallocated.
BOOL getsDeallocatedByReleasing(id object);

DetectDeallocations.m

#import <objc/runtime.h> 

static BOOL deallocFlag = NO;

static void swizzle(Class c, SEL orig, SEL patch)
{
    Method origMethod = class_getInstanceMethod(c, orig);
    Method patchMethod = class_getInstanceMethod(c, patch);
    
    BOOL added = class_addMethod(c, orig,
        method_getImplementation(patchMethod),
        method_getTypeEncoding(patchMethod));
    
    if (added) {
        class_replaceMethod(c, patch,
            method_getImplementation(origMethod),
            method_getTypeEncoding(origMethod));
        return;
    }
    
    method_exchangeImplementations(origMethod, patchMethod);
}

static id swizzledDealloc(id self, SEL _cmd)
{
    deallocFlag = YES;
    return self;
}

BOOL classGetsDeallocated(Class c, void (^block)(void))
{
    const SEL deallocSel  = @selector(dealloc);
    const SEL swizzledSel = @selector(swizzledDealloc);
    class_addMethod(c, swizzledSel, (IMP) swizzledDealloc, "@@:");
    
    swizzle(c, deallocSel, swizzledSel);
    deallocFlag = NO;
    block();
    swizzle(c, swizzledSel, deallocSel);
    
    return deallocFlag;
}

// Wouldn’t this be simply [object retainCount] == 1 for all
// cases except when somebody is doing something really stupid?
BOOL getsDeallocatedByReleasing(id object)
{
    return classGetsDeallocated([object class], ^{ [object release]; });
}