def METHOD_NAME(self):
    """
    Something that is already btrfs but is subvolid=5, indicating that it's
    a loopback. We will try to clean this up automatically, but require
    manual intervention if it could not be unmounted.
    """
    artifacts_dir = Path(tempfile.mkdtemp(prefix=self.id()))
    volume_dir = artifacts_dir / vfr.VOLUME_DIR
    os.mkdir(volume_dir)
    with tempfile.NamedTemporaryFile() as loopback:
        loopback.truncate(500 * 1024 * 1024)
        subprocess.run(["mkfs.btrfs", loopback.name], check=True)
        subprocess.run(["sudo", "mount", loopback.name, volume_dir], check=True)
        subprocess.run(
            [
                "sudo",
                "chown",
                f"{os.getuid()}:{os.geteuid()}",
                loopback.name,
                volume_dir,
            ],
            check=True,
        )
        with open(volume_dir / "force-in-use", "w") as f:
            f.write("foo")
            with self.assertRaisesRegex(
                InfraError, "appears to be a mounted btrfs"
            ):
                vfr.get_volume_for_current_repo(artifacts_dir=artifacts_dir)
        subprocess.run(["sudo", "umount", volume_dir])