def METHOD_NAME(self) -> str:
    """
    Crate a scratch subvolume on a BTRFS filesystem where we can create
    pathological test cases for volume_for_repo.py. We can't use existing
    Antlir mechanisms like TempSubvolumes, because volume_for_repo is the
    thing that sets up the environment for those to work.
    """
    repo_root = find_repo_root()
    # hopefully the parent of the repo is on a btrfs filesystem
    hopefully_btrfs = repo_root.dirname()
    scratch_path = (
        hopefully_btrfs / f"test_volume_for_repo_{self.id()}_{time.time()}"
    )
    self.addCleanup(
        lambda scratch_path: btrfsutil.delete_subvolume(
            scratch_path, recursive=True
        ),
        scratch_path,
    )
    btrfsutil.create_subvolume(scratch_path)
    subprocess.run(
        ["sudo", "chown", f"{os.getuid()}:{os.getgid()}", scratch_path], check=True
    )
    return str(scratch_path)