XCTestCase (MethodSwizzling)

XCTestCase+MethodSwizzling.h

//
//  XCTestCase+MethodSwizzling.h
//
//  Created by Diogo Tridapalli on 5/28/14.
//  Copyright (c) 2014 Diogo Tridapalli. All rights reserved.
//

#import <XCTest/XCTest.h>

@interface XCTestCase (MethodSwizzling)

- (void)swizzleClassMethod:(SEL)aOriginalMethod
                   inClass:(Class)aOriginalClass
                withMethod:(SEL)aNewMethod
                 fromClass:(Class)aNewClass
              executeBlock:(void (^)(void))aBlock;

- (void)swizzleInstanceMethod:(SEL)aOriginalMethod
                      inClass:(Class)aOriginalClass
                   withMethod:(SEL)aNewMethod
                    fromClass:(Class)aNewClass
                 executeBlock:(void (^)(void))aBlock;

@end

XCTestCase+MethodSwizzling.m

//
//  XCTestCase+MethodSwizzling.m
//
//  Created by Diogo Tridapalli on 5/28/14.
//  Copyright (c) 2014 Diogo Tridapalli. All rights reserved.
//

#import "XCTestCase+MethodSwizzling.h"
#import <objc/runtime.h>

@implementation XCTestCase (MethodSwizzling)

- (void)swizzleInstanceMethod:(SEL)aOriginalMethod
                      inClass:(Class)aOriginalClass
                   withMethod:(SEL)aNewMethod
                    fromClass:(Class)aNewClass
                 executeBlock:(void (^)(void))aBlock
{
    Method originalMethod = class_getInstanceMethod(aOriginalClass, aOriginalMethod);
    Method mockMethod = class_getInstanceMethod(aNewClass, aNewMethod);
    method_exchangeImplementations(originalMethod, mockMethod);
    aBlock();
    method_exchangeImplementations(mockMethod, originalMethod);
}

- (void)swizzleClassMethod:(SEL)aOriginalMethod
                   inClass:(Class)aOriginalClass
                withMethod:(SEL)aNewMethod
                 fromClass:(Class)aNewClass
              executeBlock:(void (^)(void))aBlock
{
    Method originalMethod = class_getClassMethod(aOriginalClass, aOriginalMethod);
    Method mockMethod = class_getClassMethod(aNewClass, aNewMethod);
    method_exchangeImplementations(originalMethod, mockMethod);
    aBlock();
    method_exchangeImplementations(mockMethod, originalMethod);
}

@end

Based on gist: https://gist.github.com/pk/1038034