Refactor plugin tests (#2273)

* refactor existing tests frmo unittest style setup and teardown to pytest fixtures (adds pytest-mock as a dep to use mocker.patch)

* Common fixture for temp directory, move everything into flat pytest fixtures

* mypy

* changes.md

Author: raghuvardhan07

CHANGES.md

@@ -8,7 +8,7 @@
 
 - Declare workflow-level `permissions: contents: read` on the 8 remaining workflows (CVE-2025-30066 hardening) `PR #2241`
 - Skip base class tests in test runs `PR #2263`
-- Transitioned from unittest.Testcase to pytest fixtures `PR #2265`
+- Transitioned from unittest.Testcase to pytest fixtures (`PR #2265`, `PR #2273`)
 - Replace MinIO Docker container with moto in-memory mock for S3 tests `PR #2272`
 
 ## Documentation

src/bandersnatch/tests/plugins/conftest.py

@@ -0,0 +1,21 @@
+from collections import defaultdict
+from pathlib import Path
+
+import pytest
+
+import bandersnatch.storage
+
+
+@pytest.fixture(autouse=True)
+def plugin_test_dir(monkeypatch: pytest.MonkeyPatch, tmp_path: Path) -> Path:
+    """
+    Automatically isolates each test into its own temp dir and
+    ensures the storage plugin registry is clean.
+    """
+    monkeypatch.setattr(
+        bandersnatch.storage,
+        "loaded_storage_plugins",
+        defaultdict(list),
+    )
+    monkeypatch.chdir(tmp_path)
+    return tmp_path