gistfile1.m

#import "SwizzlingTest.h"
#import </usr/include/objc/objc-class.h>

@interface Swizzlingee : NSObject
- (NSString *) hoge;
- (NSString *) piyo;
@end

@implementation Swizzlingee
- (NSString *)hoge
{
    static NSString *s = @"hoge";
    return s;
}

- (NSString *)piyo
{
    static NSString *s = @"piyo";
    return s;    
}

@end

@implementation SwizzlingTest

- (void)testThatSwizzled
{
    //Do swizzle
    Method hogeMethod = class_getInstanceMethod([Swizzlingee class], @selector(hoge));
    Method piyoMethod = class_getInstanceMethod([Swizzlingee class], @selector(piyo));
    method_exchangeImplementations(hogeMethod, piyoMethod);
    
    //Invoke the method
    Swizzlingee *underTest = [[Swizzlingee alloc] init];
    NSString *s = [underTest hoge];
    
    STAssertEqualObjects(s, @"piyo", @"hoge method should returns piyo after swizzled");
}
@end