test: remove anonymous volumes with short-lived test containers

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/conftest.py

@@ -12,7 +12,7 @@ from pathlib import Path
 
 import docker
 import pytest
-from helpers import Container, remove_quietly, start_container
+from helpers import Container, remove_quietly, run_once, start_container
 
 ROOT = Path(__file__).resolve().parent.parent
 IMAGE = os.environ.get("IMAGE", "restic-backup-docker:test")
@@ -108,10 +108,13 @@ def _cleanup_leftovers(docker_client: docker.DockerClient) -> Iterator[None]:
 
 @pytest.fixture(scope="session")
 def detected_features(docker_client: docker.DockerClient, image: str) -> set[str]:
-    out = docker_client.containers.run(
-        image, entrypoint=["sh", "-c", FEATURE_PROBE], remove=True, labels={"rbd-test-run": RUN_ID}
+    out = run_once(
+        docker_client,
+        image,
+        entrypoint=["sh", "-c", FEATURE_PROBE],
+        labels={"rbd-test-run": RUN_ID},
     )
-    return set(out.decode().split())
+    return set(out.split())
 
 
 def pytest_collection_modifyitems(items: list[pytest.Item]) -> None:

tests/helpers.py

@@ -135,3 +135,21 @@ def start_container(
 def remove_quietly(container: Container) -> None:
     with contextlib.suppress(docker.errors.NotFound):
         container.raw.remove(force=True, v=True)
+
+
+def run_once(client: docker.DockerClient, image: str, **kwargs: Any) -> str:
+    """Run a short-lived container and return its output.
+
+    `containers.run(remove=True)` keeps the image's anonymous volumes (VOLUME /data),
+    so run detached and remove the container together with its volumes.
+    """
+    container = client.containers.run(image, detach=True, **kwargs)
+    try:
+        result = container.wait()
+        output = container.logs(stdout=True, stderr=False).decode()
+        if result["StatusCode"] != 0:
+            raise CommandError(f"container exited {result['StatusCode']}:\n{output}")
+        return output
+    finally:
+        with contextlib.suppress(docker.errors.NotFound):
+            container.remove(force=True, v=True)

tests/test_compat.py

@@ -19,7 +19,7 @@ from types import SimpleNamespace
 import docker
 import pytest
 from conftest import LABELS
-from helpers import Container
+from helpers import Container, run_once
 
 HELLO = "backup me"
 PRE_BACKUP_HOOK = '#!/bin/sh\necho "PRE-HOOK-RAN"\n'
@@ -409,10 +409,10 @@ class TimezoneRunner:
     image: str
 
     def zone(self, env: dict[str, str] | None = None) -> str:
-        out = self.client.containers.run(
-            self.image, entrypoint=["date", "+%Z"], environment=env, remove=True, labels=LABELS
+        out = run_once(
+            self.client, self.image, entrypoint=["date", "+%Z"], environment=env, labels=LABELS
         )
-        return out.decode().strip()
+        return out.strip()
 
 
 @pytest.fixture(scope="module")