Currently, [`build_component.py`](https://github.com/SeattleTestbed/common/blob/master/build_component.py#L283) removes the contents of the build target directory before copying over files anew. This can hurt if you happen to specify the wrong target dir, or have files you created / edited in the target dir but did not commit them yet. Since it's trivial to clean / recreate the target dir before you build yourself, I think a good thing to do is to require the person starting the build perform these steps consciously. `build_component` should only complain if the target dir is not empty, but not attempt to clean it. @XuefengHuang provided a patch to the (outdated) `preparetest` script providing that functionality, see SeattleTestbed/dist#143.