tests/sitecustomize.py

help: describe what ui.tweakdefaults changes, concretely

Currently, one has to look at the code.

A couple things are suboptimal:
- probably not translatable
- lines don't get wrapped (a couple are a bit too long)
but it seems to better this way than without help at all.

Differential Revision: https://phab.mercurial-scm.org/D5187

from __future__ import absolute_import
import os

if os.environ.get('COVERAGE_PROCESS_START'):
    try:
        import coverage
        import uuid

        covpath = os.path.join(os.environ['COVERAGE_DIR'],
                               'cov.%s' % uuid.uuid1())
        cov = coverage.coverage(data_file=covpath, auto_data=True)
        cov._warn_no_data = False
        cov._warn_unimported_source = False
        cov.start()
    except ImportError:
        pass