Swizzling is not working for class methods

Swizzling is not performing dynamic method exchanging . This the code i used.i heard that it is an solution where Dependency injection unable to do in XCTest in xcode 7. can you give me explanation on Swizzling over DI(Dependency) with example ?

#import "TNUserDetail+Swizzle.h"
#import <objc/runtime.h>

@implementation TNUserDetail (Swizzle)

+ (void) swizzleInstanceSelector:(SEL)originalSelector
                 withNewSelector:(SEL)newSelector
{
    Method originalMethod = class_getClassMethod(self, originalSelector);
    Method newMethod = class_getClassMethod(self, newSelector);

    BOOL methodAdded = class_addMethod([self class],
                                       originalSelector,
                                       method_getImplementation(newMethod),
                                       method_getTypeEncoding(newMethod));

    if (methodAdded) {
        class_replaceMethod([self class],
                            newSelector,
                            method_getImplementation(originalMethod),
                            method_getTypeEncoding(originalMethod));
    } else {
        method_exchangeImplementations(originalMethod, newMethod);
    }
}

+(BOOL)isSignUpSwizzle {

    return sighUp;
}


Test
_____

@implementation TNSettingsViewControllerTests

- (void)setUp {
    [super setUp];

    UIStoryboard *sb = [UIStoryboard storyboardWithName:@"Main" bundle:nil];

    self.settingVC = [sb instantiateViewControllerWithIdentifier:@"TNSettingsViewController"];


    [self.settingVC performSelectorOnMainThread:@selector(loadView) withObject:nil waitUntilDone:YES];
    [self.settingVC performSelectorOnMainThread:@selector(viewWillAppear:) withObject:nil waitUntilDone:YES];
}

-(void)testTwitterConnectSwitchValueChanged
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{

        [TNUserDetail swizzleInstanceSelector:@selector(isSignUpWithTwitter) withNewSelector:@selector(isSignUpSwizzle)];
        [TNUserDetail isSignUpWithTwitter];
    });

    sighUp = YES;
    self.settingVC.twitterConnectSwitch.on = YES;
    [self.settingVC.twitterConnectSwitch sendActionsForControlEvents:UIControlEventValueChanged];;
}

Here when i call [TNUserDetail isSignUpWithTwitter] ,+(BOOL)isSignUpSwizzle is not being called and only actual method is being called. Whats wrong .Note both methods are class methods.

Methods instance exist in dispatch table class, but class methods exist in dispatch table meta_class so you need use 'meta class' instead self(class).

#import "TNUserDetail.h"
#import <objc/runtime.h>

@implementation TNUserDetail

+ (void)swizzleInstanceSelector:(SEL)originalSelector withNewSelector:(SEL)newSelector {
    const char *className = [NSStringFromClass(self) UTF8String];
    Class clazz = objc_getMetaClass(className);
    Method originalMethod = class_getClassMethod(clazz, originalSelector);
    Method newMethod = class_getClassMethod(clazz, newSelector);

    BOOL methodAdded = class_addMethod(clazz,
                                       originalSelector,
                                       method_getImplementation(newMethod),
                                       method_getTypeEncoding(newMethod));

    if (methodAdded) {
        class_replaceMethod(clazz,
                            newSelector,
                            method_getImplementation(originalMethod),
                            method_getTypeEncoding(originalMethod));
    } else {
        method_exchangeImplementations(originalMethod, newMethod);
    }
}

+ (void)load {
    [super load];
    [self swizzleInstanceSelector:@selector(printHello) withNewSelector:@selector(printHelloWorld)];
}

+ (void)printHello {
    NSLog(@"Hello");
}

+ (void)printHelloWorld {
    NSLog(@"Hello World");
}

@end

and call [TNUserDetail printHello]; print 'Hello World'

But your swizzling affects the entire project. For this case I recommendation use partial mocks (OCMock)