Functional testing of information in a view?

I like model tests, they make sense to me. But I still haven't quite 'got' functional testing. I'm having difficulty doing sensible testing... I quite often end up calling the same method in my tests as I do in my 'real' code, which to me feels very wrong, and seems likely to be hiding more bugs than it shows.

For example, I want to display a file size in a view. So I compare the response body against the regexp /File size : #{human_size(File.size(file))}/

What do I then paste into my view code? Almost exactly the same thing : File size : <%= human_size(File.size(@asset.file)) %>

Does anyone else think there's something wrong there? It feels a bit icky to be making my tests pass by essentially cut & pasting from my test code...

Would love to see other people's functional tests to get a better idea of what should & shouldn't be tested. Anyone willing to share?