tests: don't silence errors while creating test index "Errors should never pass silently." For example, I had the problem, that a previous test did not clean up the lock file for the index_dir, which then caused the future tests to fail. Because the error has been silenced, it took a while until I found the reason.

# requirements.txt file for use as "pip install -r requirements.txt" as a
# readthedocs compatible alternative to "pip install -e ." which is a working
# alternative to "setup.py develop" which doesn't work with Mercurial 3.7
.