单例单元测试: mock和swizzle

Question

我目前正在尝试测试一些使用AVAudioSession的代码，由于它是一个单例，我试图模拟它的尝试到目前为止已经被证明是困难的，我做了一些研究，突然想到了一个想法，让它获得它的实例，然后按照你想要的方式实际初始化你的子类，但是我很难弄清楚应该用什么方法。我尝试了sharedInstance，class_addMethod()返回yes，说明它是添加的，而不是替换的。我能用这种方式有效地模拟一个单例吗？

@interface AVAudioSessionFake : AVAudioSession

@property (readonly,    nonatomic) BOOL wasSetActiveErrorCalled;

-(instancetype)initStub;

@end

@implementation AVAudioSessionFake

+ (void)load
{
    [AVAudioSessionFake swizzleOriginalMethod:@"sharedInstance" with:@"initStub"];
}

+ (void)swizzleOriginalMethod:(NSString*)Original with:(NSString*)replacement
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^
    {
        Class class = [self class];

        SEL originalSelector = NSSelectorFromString(Original);
        SEL swizzledSelector = NSSelectorFromString(replacement);

        Method originalMethod = class_getInstanceMethod(class, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);

        BOOL didAddMethod =
        class_addMethod(class,
                      originalSelector,
                      method_getImplementation(swizzledMethod),
                      method_getTypeEncoding(swizzledMethod));

        if (didAddMethod)
        {
          class_replaceMethod(class,
                              swizzledSelector,
                              method_getImplementation(originalMethod),
                              method_getTypeEncoding(originalMethod));
        }
        else
        {
          method_exchangeImplementations(originalMethod, swizzledMethod);
        }
    });
}

-(instancetype)initStub
{
    return [[[self class]alloc]init];
}

- (BOOL)setActive:(BOOL)active error:(NSError *__autoreleasing *)outError
{
    _wasSetActiveErrorCalled = YES;

    return [super setActive:active error:outError];
}

@end

Answer 1

您可以使用sharedInstance方法返回您的AVAudioSessionFake，如下所示

#AVAudioSessionFake：

@interface AVAudioSessionFake : AVAudioSession
@property (readonly,    nonatomic) BOOL wasSetActiveErrorCalled;

@end

@implementation AVAudioSessionFake
-(instancetype)init
{
    if (self == [super init]) {
        // your init code
    }
    return self;
}
 -(BOOL)setActive:(BOOL)active error:(NSError *__autoreleasing *)outError
{
     _wasSetActiveErrorCalled = YES;

    return [super setActive:active error:outError];
}
@end

# swizzle sharedInstance：

static Method original_AVAudioSession_SharedInstance_ClassMethod;
static Method swizzled_AVAudioSession_SharedInstance_ClassMethod;
@interface AVAudioSession (AVAudioSessionSwizzledSharedInstance) 
@end
@implementation AVAudioSession (AVAudioSessionSwizzledSharedInstance)
    + (void)load
    {
        static dispatch_once_t onceToken;
        dispatch_once(&onceToken, ^
        {
          Class class = object_getClass((id)self);
         　SEL original_Selector = @selector(sharedInstance);
          SEL swizzled_Selector = @selector(swizzled_sharedInstance);
        　 original_AVAudioSession_SharedInstance_ClassMethod = class_getInstanceMethod(class, original_Selector);
          swizzled_AVAudioSession_SharedInstance_ClassMethod = class_getInstanceMethod(class, swizzled_Selector);
        });
    }
    + (void)swizzling_AVAudioSession_SharedInstance
    {    
　　　　method_exchangeImplementations(original_AVAudioSession_SharedInstance_ClassMethod,swizzled_AVAudioSession_SharedInstance_ClassMethod);
    }
    + (id)swizzled_sharedInstance 
    {
         static dispatch_once_t p = 0;
        // initialize sharedObject as nil (first call only)
        __strong static AVAudioSessionFake _sharedObject = nil;

        dispatch_once(&p, ^{
            _sharedObject = [[AVAudioSessionFake alloc] init];
        });
        return _sharedObject;
    }

#使用：

- (void)testAnAVAudioSessionMethod {
   [AVAudioSession swizzling_AVAudioSession_SharedInstance]; //Start swizzling shareInstance method
   // some test code and assert result here
   [AVAudioSession swizzling_AVAudioSession_SharedInstance]; //return original method
}

一些有用的链接The Right Way to Swizzle in Objective-C、method swizzling、another question in SO