Add test file for scripts in Tools (#13447).
Add test file for scripts in Tools (#13447).

When people find bugs in scripts such as reindent.py, msgfmt.py or
pygettext.py, we have to try to reproduce the bug manually, apply a fix
and test manually again.  The alternative is to only read the code and
trust that it works.  This test file is a way to stop that
unsatisfactory state of things and write proper unit tests instead.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator