I have a UIViewController that contains each of UITextField, UIButton and UILabel. I put something in the UITextField, press a button and the string is now capitalized in the UILabel.
My question is: how do I set up the IBAction in Swift for unit tests? If there is no way to test the action in Swift, what else can I do to test this?
In the unit-testing world, the most difficult work could be UI testing. So, what you can do is to check whatever is available to you from the API.
You can not toggle an action or event like you are a phone user. So, you have to programmatically toggle actions or events in order to test on that. You will also have to programmatically initialize the UI elements yourself.
IBAction is just nothing but an indicator to tell UIStoryboard that this is a connector method, you can ignore and treat it as a normal method.