There are many cases where developers want tests to run only when some prerequisites are satisfied - such as if running on a specific OS, some http server is available etc.
junit-ext is an open source addon for junit 4.x to help running tests conditionally.
It adds the runner "PrerequisiteAwareClassRunner", along with the annotation "@Prerequisites" and a few Checkers to help a developers to easily get their things like - FileChecker, OSChecker, HttpCheker and so on.
Features in junit-ext
junit-ext is available at http://code.google.com/p/junit-ext/