> For Windows I'm getting a more informative error message than from the
> buildbot output if I run the test via an ssh client:

Try with my last patch (pythonrun_filename_decoding_test.patch). It
fixes also fail on Linux with 8-bit locale.

$ LC_ALL=en_US.ISO-8859-1 LANG=en_US.ISO-8859-1 LANGUAGE= ./python -m
test -m test_non_utf8 test_cmd_line_script
[1/1] test_cmd_line_script
test test_cmd_line_script failed -- Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/test/test_cmd_line_script.py", line
373, in test_non_utf8
    importlib.machinery.SourceFileLoader)
  File "/home/serhiy/py/cpython/Lib/test/test_cmd_line_script.py", line
129, in _check_script
    expected_package, expected_loader)
  File "/home/serhiy/py/cpython/Lib/test/test_cmd_line_script.py", line
113, in _check_output
    self.assertIn(printed_file.encode('utf-8'), data)
AssertionError: b"__file__=='/tmp/tmpda64hd/\\udcf1\\udcea\\udcf0\\udce8
\\udcef\\udcf2.py'" not found in b"__loader__==<class
'_frozen_importlib.SourceFileLoader'>\n__file__=='/tmp/tmpda64hd/\\xf1\
\xea\\xf0\\xe8\\xef\\xf2.py'\n__package__==None
\nsys.argv[0]=='/tmp/tmpda64hd/\\xf1\\xea\\xf0\\xe8\\xef\
\xf2.py'\nsys.path[0]=='/tmp/tmpda64hd'\ncwd=='/home/serhiy/py/cpython/build/test_python_3546'\n"