Use this file template instead of Apple's "Objective-C test case class" template. An explanation of the benefits is on Quality Coding at Warning: Don't Use Apple's Template for Unit Tests.
make install to install the templates. (You can make uninstall if you change your mind.) Relaunch Xcode, and you should see "OCUnit test case" listed in the File Template Library in the Utilities pane — one for iOS, and one for OS X. You can also find them in the "New File" templates under Cocoa Touch and Cocoa.