How to initialize a subclass when the init method of the superclass is NS_UNAVAILABLE - objective-c

Question

I'm attempting to write a test for an objective-c class. The class I'm trying to test is MyClass and it looks like this:
#interface MyClass : NSObject
- (void)dispatchEvent:(IMAAdEvent *)event;
#end
In order to test this dispatchEvent method, I need to pass in an instance of IMAAdEvent. The IMAAdEvent class comes from Google's library GoogleAds-IMA-iOS-SDK.
Unfortunately, I can't call init on this class because the init method is marked as NS_UNAVAILABLE. In XCode I get an error that reflects this:
'init' in unavailable
Ideally, I would like to make my own mock subclass of IMAAdEvent like this. Is there some way I can initialize my subclass without calling the unavailable init method on the superclass?:
#interface MockImaAdEvent : IMAAdEvent
#end
#implementation MockImaAdEvent
- (id)init {
// is there something I can do here so that I return an instances
// of the subclass without calling [super init]?
}
#end

Answer 1

As of Xcode 12.5, Swift is no longer able to use the previous solution. The compiler has started returning errors for init() is unavailable on lines of code where new init functions have been added. The Xcode 12.5 Release Notes indicate the following:
Clang now infers the availability of +new from availability annotations on -init methods. Since +new calls [[Foo alloc] init], +new isn’t available unless +init is available.
Despite this release note, there is still a valid workaround. By writing the mock class in Objective-C and using a bridging-header to bring it into Swift, the mock class can still call super.new to get a new instance of the parent class (and then customize the subclass from there).
Here is an example:
#interface MockInAppMessagingCampaignInfo ()
#property (strong, nonatomic) NSString *campaignNameValue;
#end
#implementation MockInAppMessagingCampaignInfo
+ (id)newWithCampaignName:(NSString *)campaignName {
MockInAppMessagingCampaignInfo *newObject = super.new;
newObject.campaignNameValue = campaignName;
return newObject;
}
- (NSString *)campaignName {
self.campaignNameWasCalled = YES;
return self.campaignNameValue ?: #"";
}
#end

Answer 2

If I use a method that's not called init then this seems to work. It still seems really weird to not call [super init] in this function, but it's working and returning a new instance of the MockImaAdEvent class
#interface MockImaAdEvent : IMAAdEvent {
enum IMAAdEventType type;
}
#property (nonatomic) enum IMAAdEventType type;
#end
#implementation MockImaAdEvent
#synthesize type;
- (id)initWithType:(NSInteger)_type {
type = _type;
return self;
}
#end
// in my test I can initialize like this:
MockImaAdEvent *adEvent = [[MockImaAdEvent alloc] initWithType:kIMAAdEvent_LOADED];

Answer 3

An alternative solution for Xcode 12.5 that doesn't require Objective-C bridging-header is to create a custom static initialiser that uses the objc runtime to invoke new.
I have used that for fakes that subclass objects with unavailable initialisers and works great.
Example:
static func customInit() -> SomeObjectFake {
let instance = SomeObjectFake.perform(NSSelectorFromString("new")).takeRetainedValue() as! SomeObjectFake
...
return instance
}