The question of „which test cases are to automate“ is a core question in a QA-project. To answer this question properly means saving a lot of money.
In my experience there are four core criteria to help you answer this question properly. I call them the STEW criteria – on the one hand it’s an acronym for the criterias and on the other hand it’s paying attribute to Simon STEWart, the creator of Selenium Webdriver. It’s really simple and nothing more than:
Stable: Don’t waste time on automating regression tests for features, that are planned yet for redesign in the next sprint.
Troubling: Choose to automate test cases for features that are often failing in regression tests or that frequently trouble the build process.
Easy: Choose test cases, that are easy to automate, compared to manual testing. E.g. don’t automate visual comparision of bleeding edge grafics.
Worth: Don’t automate test-cases that aren’t worth it in respect to business goals. E.g. a test-case for a special feature of an enterprises local website in Cyprus isn’t worth it – sorry to all Cypriot readers.
That’s it!