I created a new Cocoa Touch Static Library project with Unit Testing in XCode 4 and added a category:
// NSString+Inflections.h
@interface NSString (Inflect
Edit: Be sure to see this answer about unit test not finding files
+1 For uploading the project. The problem is your test target does not include NSString+Inflections.m in the Build Phases.
In XCode 4
You should then get something similar the following output
TestSuite '/blahblah/PoppyTests.octest(Tests)' finished at 2011-03-28 21:31:34 +0000. Executed 1 test, with 1 failure (0 unexpected) in 0.000 (0.002) seconds