def testPushOverlays(self):
    """Test _PushOverlays."""
    self.PatchObject(os.path, 'isdir', return_value=True)
    mock_push_change = self.PatchObject(cros_mark_as_stable, 'PushChange')

    cros_mark_as_stable._PushOverlays(
        self._push_options, self._overlays, self._overlay_tracking_branch)
    self.assertEqual(mock_push_change.call_count, 3)