tests/sitecustomize.py

run-tests: make code coverage work on Python 3

This code path was obviously not tested on Python 3 because it
blew up in several places due to str/bytes mismatch.

For internal code, we normalize paths to bytes.

For code calling into `coverage`, we normalize paths to str,
which is what `coverage` seems to expect.

After this, `run-tests.py -H` works on Python 3!

Differential Revision: https://phab.mercurial-scm.org/D7133

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