I like the flutter widget test approach (it't not unique, but it's well executed there): https://flutter.io/docs/testing#widget-testing

In flutter parlance, a whole view (page/screen) is a widget, and that's the granularity I was testing it - it's good for testing the high level patterns that the screen is meant to adhere to, e.g. Send button appears when there is some text to send.

You can also have golden images for rendering of each screen. They change a lot, but that at least forces developers to look at the changes each time and decide if they're on purpose.