tests/test_bmap_helpers.py: avoid build failure from disorderfs

When running under disorderfs --shuffle-dirents=yes, the following Python code
fails:

with TemporaryDirectory(prefix="testdir_", dir=".") as directory:
    fobj = tempfile.NamedTemporaryFile(
        "r", delete=False, dir=directory
    )

Traceback (most recent call last):
  File "/tmp/disorder/test.py", line 4, in <module>
    with TemporaryDirectory(prefix="testdir_", dir=".") as directory:
  File "/usr/lib/python3.11/tempfile.py", line 1052, in __exit__
    self.cleanup()
  File "/usr/lib/python3.11/tempfile.py", line 1056, in cleanup
    self._rmtree(self.name, ignore_errors=self._ignore_cleanup_errors)
  File "/usr/lib/python3.11/tempfile.py", line 1038, in _rmtree
    _rmtree(name, onerror=onerror)
  File "/usr/lib/python3.11/shutil.py", line 738, in rmtree
    onerror(os.rmdir, path, sys.exc_info())
  File "/usr/lib/python3.11/shutil.py", line 736, in rmtree
    os.rmdir(path, dir_fd=dir_fd)
OSError: [Errno 39] Directory not empty: './testdir_6jhyg1o6'

From investigating this, the reason that the test fails when using
`disorderfs` is that, by default, FUSE overlay filesystems (of which
`disorderfs` is an instance) don't immediately delete open files
completely from the directory they are in; instead they're renamed to a
temporary dotfile name, as documented here:
http://libfuse.github.io/doxygen/structfuse__config.html#af32ff56fa1131da899756cc352718101

That causes the test to fail, because Python's `TemporaryDirectory`
context-handler quite reasonably thinks that it has removed all the
files in the directory, and therefore attempts a delete-only-if-empty
operation.  This currently fails under `disorderfs`, because the `fobj`
file is open for reading, and therefore isn't entirely deleted, but only
renamed.

Closing the file is a simple fix for this.

Note also: the `disorderfs` command-line can accept an `-o hard_remove`
option to enable FUSE `hard_remove` option, causing deletes to apply
directly to the underlying filesystem.  I've filed a request/suggestion
at https://bugs.debian.org/1093768 to enable it by default in
`disorderfs` -- but doing so apparently causes other, potentially more
disruptive, side-effects, so there's no guarantee that that behaviour
will become the default.

Thanks: James Addison <[email protected]>

Author: josch

tests/test_bmap_helpers.py

@@ -64,13 +64,13 @@ def test_get_file_system_type_symlink(self):
         """Check a file system type is returned when used with a symlink"""
 
         with TemporaryDirectory(prefix="testdir_", dir=".") as directory:
-            fobj = tempfile.NamedTemporaryFile(
+            with tempfile.NamedTemporaryFile(
                 "r", prefix="testfile_", delete=False, dir=directory, suffix=".img"
-            )
-            lnk = os.path.join(directory, "test_symlink")
-            os.symlink(fobj.name, lnk)
-            fstype = BmapHelpers.get_file_system_type(lnk)
-            self.assertTrue(fstype)
+            ) as fobj:
+                lnk = os.path.join(directory, "test_symlink")
+                os.symlink(fobj.name, lnk)
+                fstype = BmapHelpers.get_file_system_type(lnk)
+                self.assertTrue(fstype)
 
     def test_is_zfs_configuration_compatible_enabled(self):
         """Check compatibility check is true when zfs param is set correctly"""