Actually, I think I do know why it fails. in `RACSwizzleClass`, the class we're attempting to swizzle in the signalForSelector, KVO, signalForSelector case is `NSKVONotifying_RACTestObject_RACSelectorSignal`. So it has the RAC suffix. But this class /itself/ doesn't implement the selector we're turning into a signal. It's actually this class's superclass, RACTestObject_RACSelectorSignal.

I wonder what would happen if KVO added a suffix rather than a prefix?