Dinamic hook of object's method exaple

gistfile1.m

@interface SimpleHookExampleClass : NSObject

@property (nonatomic) NSUInteger state;

@end

@implementation SimpleHookExampleClass

- (NSUInteger)mutStateOnArg:(NSUInteger)arg
{
    return _state * arg;
}

@end

- (void)testSimpleExample
{
    //test observing existing method
    {
        __block BOOL hookWasCalled = NO;
        
        NSUInteger originalArg   = 12;
        NSUInteger originalState = 2;
        
        typedef NSUInteger(^BlockObserver)(id _self, NSUInteger arg);
        
        id observer = ^BlockObserver(BlockObserver(^previousImplementationGetter)(void)) {
            
            return ^NSUInteger(id _self, NSUInteger arg) {
                
                hookWasCalled = YES;
                
                BlockObserver previousImplementation = previousImplementationGetter();
                
                NSUInteger previousResult = previousImplementation(_self, arg);
                
                STAssertEquals((NSUInteger)24, previousResult, nil);
                
                STAssertEquals((NSUInteger)12, arg, nil);
                return 11;
            };
        };
        
        SimpleHookExampleClass *testObject = [SimpleHookExampleClass new];
        
        testObject.state = originalState;
        
        [testObject addMethodHook:observer
                         selector:@selector(mutStateOnArg:)];
        
        NSUInteger result = [testObject mutStateOnArg:originalArg];
        
        STAssertEquals((NSUInteger)11, result, nil);
        
        STAssertTrue(hookWasCalled, nil);
    }
    
    //test normal call
    {
        NSUInteger originalArg   = 10;
        NSUInteger originalState = 3;
        
        __weak TestClassToTestHooks *weakTestObject;
        @autoreleasepool
        {
            TestClassToTestHooks *testObject = [TestClassToTestHooks new];
            weakTestObject = testObject;
            
            testObject.state = originalState;
            
            id result = [testObject returnObjectForIntegerPoint:NSMakeRange(2, 3) arg:originalArg];
            
            STAssertEqualObjects([@(originalArg * originalState) stringValue], result, nil);
        }
        STAssertNil(weakTestObject, nil);
    }
}