Calling a method on the main thread?

Here is a better way to do this in Swift:

runThisInMainThread { () -> Void in
    // Run your code
    self.doSomething()
}

func runThisInMainThread(block: dispatch_block_t) {
    dispatch_async(dispatch_get_main_queue(), block)
}

Its included as a standard function in my repo, check it out: https://github.com/goktugyil/EZSwiftExtensions

There's a saying in software that adding a layer of indirection will fix almost anything.

Have the doSomething method be an indirection shell that only does a performSelectorOnMainThread to call the really_doSomething method to do the actual Something work. Or, if you don't want to change your doSomething method, have the mock test unit call a doSomething_redirect_shell method to do something similar.

Objective-C

dispatch_async(dispatch_get_main_queue(), ^{
    [self doSomething];
});

Swift

DispatchQueue.main.async {
    self.doSomething()
}

Legacy Swift

dispatch_async(dispatch_get_main_queue()) {
    self.doSomething()
}