Hm, actually there is a possibility to test the appearance of a toast. Simply create a subclass of Toast (e.g. MyOwnToast) and use this one in your program instead of Toast. In this subclass you can overwrite the show() method to notify you, that the Toast is being shown.
Additionally you can store the Toast within the show() method in kind of a ToastDatabase singleton from where you can access the Toast and it's view also after it has been shown and destroyed (haven't tested this with Toasts, but I often do that with the result intents of activities to keep them available for further tests after they have been destroyed - so it should be no problem to implement this with Toasts).
Beware: maybe you have to clone the Toast object or it's corresponding view for the ToastDatabase because probably it will be null after the Toast has been destroyed. Hope this helps!