mozilla/addon-sdk — pull request #582 by Mossop (2012-09-19 17:21:30+00:00)
Title: Only launch the app if there are actually tests to be run.

If you run tests with a filter in place to run say just a single test file from addon-kit, cfx still launches the app for api-utils and test-harness tests even though nothing will actually get run. This just makes cfx abandon launching when there is nothing to be tested.