You need to add the files below, and do this in @Before (as mentioned in https://gist.github.com/marsucsb/6059760)
ActionBarSherlock.registerImplementation(ActionBarSherlockRobolectric.class);
ActionBarSherlock.unregisterImplementation(ActionBarSherlockNative.class);
ActionBarSherlock.unregisterImplementation(ActionBarSherlockCompat.class);