I too struggle with this. I did make some rules focusing on *Test.cs files but that it didn't work because it was still too general (and turned them off). I have found that I need a set of rules in my test project that are different from distributable (aka
production) code. I also use lowercase for test helpers but can't restrict this rule only to the test library (and I don't want to use suffix or prefix on the file name).
Love resharper, they nicely provide licenses for this project too. Soooo I headed off to youtrack.jetbrains.net and I can't find a bug or feature request. I tried searches around Resharper product and "code inspection" and various other words like underline.
So I have put in a feature request here http://youtrack.jetbrains.net/issue/RSRP-276635
While you are there how about voting for this: http://youtrack.jetbrains.net/issue/RSRP-47805?projectKey=RSRP&query=code+inspection