I found lots of material on how to conduct UI tests using the Espresso framework and others. However, I am struggling to find any information that tells me to what extent should I test the UI: should I write tests that test every possible GridItem in every gridView? Just the items that are clickable? How should I go about determining what, and in how in depth I should test any given Android UI?
For this question, you should assume that you are the developer, the owner, and the designer.
It would be nice to get something that gets at what to prioritize in the general case.