Features of subscriptions testing in iOS

I want to talk about the features of subscriptions testing in iOS, depending on the types of subscriptions and a life-cycle. Lift the veil of the black box and show how the recipe looks like, what useful information it contains for the tester and how it will help you in your work. I'd like to share features, and, probably, to save someone time and prevent problems by sharing my experience and observations when testing subscriptions.