My experience has been that functional tests are excellent and discovering that "something" is wrong, but less good at finding what is actually broken. Say my

My experience has been that functional tests are excellent and discovering that "something" is wrong, but less good at finding what is actually broken. Say my "log in" test fails: OK, I know auth is broken... but what part of it? Is there some JavaScript hijacking the form submission? Is my login view busted? Do I have an error in my authorization system itself? Is the LDAP server I'm authorizing against down? Has someone changed the schema? Etc., etc., etc. I do find functional tests to be a pretty valuable part of my testing toolkit, but unit tests seem to get me a bigger "bang for my buck", so functional tests tend to be something I don't spend a ton of time working on. (I wish I did write more functional tests, but clearly they're not valuable enough for me to prioritize them. Otherwise I'd already be using 'em more.)