"""
On ext4 this creates 4 different files: ['\u03d4', '\u03d2\u0308', '\u03ab', '\u03a5\u0308']
On ZFS with utf8only=true (and I believe normalization=formD), only 2 files are created but each of the 4 filenames can be used to access either of the 2 files.
This is also the default behavior on Mac.

The test is already skipped on darwin (Lib/test/test_unicode_file_functions.py:120), and should be skipped for ZFS too (might depend on the exact flags used), however we weren't able to find a portable way to determine the filesystem and flags.
"""

I suggest to create a temporary directory, create the 4 files and see how many files you can using os.listdir(). If you get 4, the FS doesn't normalize anything. If you get less, it's likely that the FS normalizes names.