Add mock file audit backend

tests/test_mock_file_backend.py

@@ -0,0 +1,56 @@
+from __future__ import annotations
+
+import json
+import os
+from datetime import datetime, timedelta, timezone
+
+from audit_core.interface import AuditEvent
+from audit_core.mock_file_backend import MockFileAuditBackend
+
+
+def test_emit_writes_hourly_jsonl_file(tmp_path):
+    now = datetime(2026, 6, 1, 20, 30, tzinfo=timezone.utc)
+    backend = MockFileAuditBackend(base_dir=tmp_path, now=now)
+
+    path = backend.emit(
+        AuditEvent(
+            source="openbao",
+            action="audit.verify",
+            resource="openbao/openbao-0",
+            outcome="success",
+            details={"file_audit_visible": True},
+        )
+    )
+
+    assert path.endswith("audit-20260601T20.jsonl")
+    lines = (tmp_path / "audit-20260601T20.jsonl").read_text(encoding="utf-8").splitlines()
+    assert len(lines) == 1
+    record = json.loads(lines[0])
+    assert record["source"] == "openbao"
+    assert record["tenant"] == "platform"
+    assert record["scope"] == "platform-control-plane"
+    assert record["details"] == {"file_audit_visible": True}
+
+
+def test_cleanup_removes_files_older_than_retention(tmp_path):
+    now = datetime(2026, 6, 8, 20, 30, tzinfo=timezone.utc)
+    old_file = tmp_path / "audit-20260531T20.jsonl"
+    fresh_file = tmp_path / "audit-20260608T20.jsonl"
+    ignored_file = tmp_path / "other.jsonl"
+    old_file.write_text("{}\n", encoding="utf-8")
+    fresh_file.write_text("{}\n", encoding="utf-8")
+    ignored_file.write_text("{}\n", encoding="utf-8")
+
+    old_ts = (now - timedelta(days=8)).timestamp()
+    fresh_ts = (now - timedelta(days=1)).timestamp()
+    os.utime(old_file, (old_ts, old_ts))
+    os.utime(fresh_file, (fresh_ts, fresh_ts))
+
+    backend = MockFileAuditBackend(base_dir=tmp_path, retention_days=7, now=now)
+
+    removed = backend.cleanup_old_files()
+
+    assert str(old_file) in removed
+    assert not old_file.exists()
+    assert fresh_file.exists()
+    assert ignored_file.exists()