mirror of
https://github.com/kevinveenbirkenbach/docker-volume-backup.git
synced 2026-10-20 01:43:25 +00:00
Kevin Veen-Birkenbach
0735e5fa7b
The zfs snapshot was read through <subject>/.zfs/snapshot/<name>. The kernel automounts that directory through a usermode helper that runs in the host's mount namespace, so a containerised baudolo never sees the mount and finds no snapshot. The snapshot is now mounted explicitly at <subject>/.baudolo-<tag>, beside where btrfs carves its own, and removed in order: umount, rmdir, zfs destroy. A failed mount destroys the snapshot at once instead of leaking one per run. The e2e suite could not reach this code at all: zpool create on the /img file failed with "no such pool or dataset", because the kernel opens vdevs from a taskq thread that resolves paths in the host's root, where the container's /img does not exist. The pool now sits on a loop device, whose /dev/loopN node the kernel creates on the host as well, and it is destroyed on exit once this script created it, since a pool is kernel-wide. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
216 lines
7.3 KiB
Python
216 lines
7.3 KiB
Python
"""Contract of the filesystem snapshot used to capture volumes atomically."""
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from __future__ import annotations
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import unittest
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from baudolo.backup.shell import BackupError
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from baudolo.backup.snapshot import SnapshotError, volume_snapshot
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class Runner:
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def __init__(self, replies: dict[str, list[str]] | None = None) -> None:
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self.calls: list[list[str]] = []
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self.replies = replies or {}
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def __call__(self, command: list[str]) -> list[str]:
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self.calls.append(list(command))
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for prefix, reply in self.replies.items():
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if " ".join(command).startswith(prefix):
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return reply
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return []
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class Unmountable(Runner):
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def __call__(self, command: list[str]) -> list[str]:
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result = super().__call__(command)
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if command[0] == "mount":
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raise BackupError("permission denied")
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return result
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class TestBtrfs(unittest.TestCase):
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def test_it_creates_a_read_only_snapshot_inside_the_subject(self) -> None:
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run = Runner()
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with volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=run):
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pass
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self.assertEqual(
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run.calls[0],
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[
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"btrfs",
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"subvolume",
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"snapshot",
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"-r",
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"/var/lib/docker",
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"/var/lib/docker/.baudolo-20260731",
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],
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)
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def test_it_removes_the_snapshot_afterwards(self) -> None:
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run = Runner()
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with volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=run):
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pass
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self.assertEqual(
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run.calls[-1],
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["btrfs", "subvolume", "delete", "/var/lib/docker/.baudolo-20260731"],
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)
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def test_it_maps_a_volume_path_into_the_snapshot(self) -> None:
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run = Runner()
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with volume_snapshot(
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"btrfs", "/var/lib/docker", "20260731", run=run
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) as resolve:
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self.assertEqual(
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resolve("/var/lib/docker/volumes/postgres_data/_data"),
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"/var/lib/docker/.baudolo-20260731/volumes/postgres_data/_data",
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)
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def test_it_keeps_the_trailing_slash_rsync_reads_as_contents(self) -> None:
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run = Runner()
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with volume_snapshot(
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"btrfs", "/var/lib/docker", "20260731", run=run
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) as resolve:
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self.assertEqual(
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resolve("/var/lib/docker/volumes/postgres_data/_data/"),
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"/var/lib/docker/.baudolo-20260731/volumes/postgres_data/_data/",
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)
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def test_it_removes_the_snapshot_even_when_the_body_raises(self) -> None:
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run = Runner()
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with (
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self.assertRaises(ZeroDivisionError),
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volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=run),
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):
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raise ZeroDivisionError
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self.assertEqual(run.calls[-1][:3], ["btrfs", "subvolume", "delete"])
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class TestZfs(unittest.TestCase):
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def _run(self) -> Runner:
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return Runner({"zfs list": ["tank/docker"]})
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def test_it_snapshots_the_dataset_mounted_at_the_subject(self) -> None:
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run = self._run()
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with volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run):
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pass
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self.assertIn(["zfs", "snapshot", "tank/docker@baudolo-20260731"], run.calls)
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def test_it_destroys_the_snapshot_afterwards(self) -> None:
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run = self._run()
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with volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run):
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pass
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self.assertEqual(
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run.calls[-1], ["zfs", "destroy", "tank/docker@baudolo-20260731"]
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)
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def test_it_mounts_the_snapshot_inside_the_subject(self) -> None:
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run = self._run()
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with volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run):
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pass
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self.assertIn(
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[
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"mount",
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"-t",
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"zfs",
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"tank/docker@baudolo-20260731",
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"/var/lib/docker/.baudolo-20260731",
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],
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run.calls,
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)
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def test_it_maps_a_volume_path_into_the_mounted_snapshot(self) -> None:
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run = self._run()
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with volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run) as resolve:
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self.assertEqual(
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resolve("/var/lib/docker/volumes/postgres_data/_data"),
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"/var/lib/docker/.baudolo-20260731/volumes/postgres_data/_data",
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)
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def test_it_unmounts_before_it_destroys(self) -> None:
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run = self._run()
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with volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run):
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pass
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self.assertEqual(
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run.calls[-3:],
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[
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["umount", "/var/lib/docker/.baudolo-20260731"],
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["rmdir", "/var/lib/docker/.baudolo-20260731"],
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["zfs", "destroy", "tank/docker@baudolo-20260731"],
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],
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)
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def test_a_failed_mount_leaves_no_snapshot_behind(self) -> None:
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run = Unmountable({"zfs list": ["tank/docker"]})
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with (
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self.assertRaises(BackupError),
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volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run),
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):
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pass
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self.assertEqual(
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run.calls[-2:],
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[
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["rmdir", "/var/lib/docker/.baudolo-20260731"],
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["zfs", "destroy", "tank/docker@baudolo-20260731"],
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],
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)
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def test_an_unmounted_dataset_is_an_error(self) -> None:
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run = Runner({"zfs list": [""]})
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with (
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self.assertRaises(SnapshotError),
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volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run),
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):
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pass
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class TestRejections(unittest.TestCase):
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def test_an_unknown_kind_is_rejected(self) -> None:
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run = Runner()
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with (
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self.assertRaises(SnapshotError),
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volume_snapshot("ext4", "/var/lib/docker", "20260731", run=run),
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):
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pass
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self.assertEqual(run.calls, [])
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def test_a_path_outside_the_subject_is_rejected(self) -> None:
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run = Runner()
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with (
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volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=run) as resolve,
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self.assertRaises(SnapshotError),
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):
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resolve("/etc/passwd")
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def test_the_subject_itself_resolves_to_the_snapshot_root(self) -> None:
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run = Runner()
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with volume_snapshot(
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"btrfs", "/var/lib/docker", "20260731", run=run
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) as resolve:
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self.assertEqual(
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resolve("/var/lib/docker"), "/var/lib/docker/.baudolo-20260731"
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)
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class Busy(Runner):
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def __call__(self, command: list[str]) -> list[str]:
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if command[:3] == ["btrfs", "subvolume", "delete"]:
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raise BackupError("target is busy")
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return super().__call__(command)
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class TestRemovalFailure(unittest.TestCase):
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def test_a_failed_removal_does_not_fail_a_completed_run(self) -> None:
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with volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=Busy()):
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pass
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def test_a_failed_removal_does_not_mask_the_body(self) -> None:
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with (
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self.assertRaises(ZeroDivisionError),
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volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=Busy()),
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):
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raise ZeroDivisionError
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if __name__ == "__main__":
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unittest.main()
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