tests: make test-check-module-imports more robust It failed for me without this in this way: tests/test-commandserver.t:19: relative import of stdlib module tests/test-lfs-serve.t:108: relative import of stdlib module tests/test-lfs-serve.t:255: relative import of stdlib module tests/test-lfs-serve.t:362: relative import of stdlib module tests/test-lfs-serve.t:406: relative import of stdlib module tests/test-lock.py:9: imports not lexically sorted: silenttestrunner < unittest, True, True tests/test-lrucachedict.py:5: imports not lexically sorted: silenttestrunner < unittest, True, True tests/test-match.py:5: imports not lexically sorted: silenttestrunner < unittest, True, True tests/test-remotefilelog-datapack.py:15: imports not lexically sorted: silenttestrunner < unittest, True, True tests/test-remotefilelog-histpack.py:14: imports not lexically sorted: silenttestrunner < unittest, True, True tests/test-simplekeyvaluefile.py:4: imports not lexically sorted: silenttestrunner < unittest, True, True tests/test-sshserver.py:6: imports not lexically sorted: silenttestrunner < unittest, True, True This is because every module is considered a stdlib module, because the stdlib_prefixes is /usr, and my repo is in /usr/local/home, which means that sys.path contains a couple of /usr/local/home/../hg/.. entries that count as "in the stdlib". Fix this by preventing any path in sys.path that's inside the mercurial source from being considered "in the stdlib". Differential Revision: https://phab.mercurial-scm.org/D5294