Inconsistent test validation on Win10

[sfaleron]

Running test_semidbm2.py results in 0, 1, or 2 errors.
The errors are always OSError: can't rename file, error: 1175
I'm using the Official Build from python.org. The semidbm2 version was from the master branch today, 20210517.
FWIW, running under Cygwin on the same machine does not seem to fail, or at least the rate is much smaller :/, although the noisy warnings are pretty much the same.

Full capture:

(venv) λ python -VV
Python 3.9.2 (tags/v3.9.2:1a79785, Feb 19 2021, 13:44:55) [MSC v.1928 64 bit (AMD64)]

(venv) λ python test_semidbm2.py
.............C:\Users\chrifull\AppData\Local\Programs\Python\Python39\lib\traceback.py:220: ResourceWarning: unclosed file <_io.BufferedReader name='C:\\Users\\chrifull\\AppData\\Local\\Temp\\semidbm_utuvljr1u9\\myfile.db\\data'>
  tb.tb_frame.clear()
ResourceWarning: Enable tracemalloc to get the object allocation traceback
..C:\Users\chrifull\dev\semidbm2\test_semidbm2.py:246: ResourceWarning: unclosed file <_io.TextIOWrapper name='C:\\Users\\chrifull\\AppData\\Local\\Temp\\semidbm_utc0z4darw\\myfile.db\\data' mode='r' encoding='cp1252'>
  self.assertEqual(len(open(db._data_filename).read()), 8)
ResourceWarning: Enable tracemalloc to get the object allocation traceback
.......C:\Users\chrifull\AppData\Local\Programs\Python\Python39\lib\traceback.py:220: ResourceWarning: unclosed file <_io.BufferedReader name='C:\\Users\\chrifull\\AppData\\Local\\Temp\\semidbm_ut7als9tb_\\myfile.db\\data'>
  tb.tb_frame.clear()
ResourceWarning: Enable tracemalloc to get the object allocation traceback
............C:\Users\chrifull\dev\semidbm2\test_semidbm2.py:301: DeprecationWarning: Please use assertEqual instead.
  self.assertEquals(db2["foobar"], b"foobar")
.......C:\Users\chrifull\dev\semidbm2\test_semidbm2.py:246: ResourceWarning: unclosed file <_io.TextIOWrapper name='C:\\Users\\chrifull\\AppData\\Local\\Temp\\semidbm_uthr2ra6nk\\myfile.db\\data' mode='r' encoding='cp1252'>
  self.assertEqual(len(open(db._data_filename).read()), 8)
ResourceWarning: Enable tracemalloc to get the object allocation traceback
........................C:\Users\chrifull\AppData\Local\Programs\Python\Python39\lib\traceback.py:220: ResourceWarning: unclosed file <_io.BufferedReader name='C:\\Users\\chrifull\\AppData\\Local\\Temp\\semidbm_utypsva8e4\\myfile.db\\data'>

  tb.tb_frame.clear()
ResourceWarning: Enable tracemalloc to get the object allocation traceback
..C:\Users\chrifull\dev\semidbm2\test_semidbm2.py:246: ResourceWarning: unclosed file <_io.TextIOWrapper name='C:\\Users\\chrifull\\AppData\\Local\\Temp\\semidbm_ut_f1klsho\\myfile.db\\data' mode='r' encoding='cp1252'>
  self.assertEqual(len(open(db._data_filename).read()), 8)
ResourceWarning: Enable tracemalloc to get the object allocation traceback
..E....C:\Users\chrifull\AppData\Local\Programs\Python\Python39\lib\traceback.py:220: ResourceWarning: unclosed file <_io.BufferedReader name='C:\\Users\\chrifull\\AppData\\Local\\Temp\\semidbm_utf8xj3s8b\\myfile.db\\data'>
  tb.tb_frame.clear()
ResourceWarning: Enable tracemalloc to get the object allocation traceback
....................
======================================================================
ERROR: test_compaction_does_not_leave_behind_files (__main__.TestWithChecksumsOn)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Users\chrifull\dev\semidbm2\test_semidbm2.py", line 198, in test_compaction_does_not_leave_behind_files
    db2.compact()
  File "C:\Users\chrifull\dev\semidbm2\semidbm2\db.py", line 251, in compact
    self._renamer(new_db._data_filename, self._data_filename)
  File "C:\Users\chrifull\dev\semidbm2\semidbm2\db.py", line 325, in __call__
    semidbm2.win32.rename(from_file, to_file)
  File "C:\Users\chrifull\dev\semidbm2\semidbm2\win32.py", line 21, in rename
    raise OSError("can't rename file, error: %s" % kernel32.GetLastError())
OSError: can't rename file, error: 1175

----------------------------------------------------------------------
Ran 94 tests in 1.144s

FAILED (errors=1)

[JelleZijlstra]

Error 1175 is apparently ERROR_UNABLE_TO_REMOVE_REPLACED. We don't generally use Windows so I don't have much insight here, sorry. It could be a local permissions issue.