chore: add simple tests for existing-policy flag

Signed-off-by: Demolus13 <[email protected]>

Author: Demolus13

tests/policy_engine/test_existing_policy.py

@@ -0,0 +1,61 @@
+# Copyright (c) 2025 - 2025, Oracle and/or its affiliates. All rights reserved.
+# Licensed under the Universal Permissive License v 1.0 as shown at https://oss.oracle.com/licenses/upl/.
+
+"""This module tests the existing-policy flag supported by the policy engine."""
+
+import argparse
+import os
+from pathlib import Path
+from unittest.mock import MagicMock, patch
+
+from macaron.__main__ import verify_policy
+
+
+def test_verify_existing_policy_success(tmp_path: Path) -> None:
+    """When an existing policy is provided and package-url is valid, verify_policy returns EX_OK."""
+    db_file = tmp_path / "macaron.db"
+    db_file.write_text("")
+
+    # Use a MagicMock for the handler.
+    mock_handler = MagicMock()
+
+    # Fake run_policy_engine and generate_vsa that returns a fixed result.
+    fake_run = MagicMock(return_value={"passed_policies": [["check-component"]], "failed_policies": []})
+    fake_generate_vsa = MagicMock(return_value=None)
+
+    # Fake PolicyReporter class: when called, returns an instance with generate method.
+    fake_policy_reporter_cls = MagicMock()
+    fake_policy_reporter_inst = MagicMock()
+    fake_policy_reporter_inst.generate.return_value = None
+    fake_policy_reporter_cls.return_value = fake_policy_reporter_inst
+
+    with (
+        patch("macaron.__main__.run_policy_engine", fake_run),
+        patch("macaron.__main__.generate_vsa", fake_generate_vsa),
+        patch("macaron.__main__.access_handler.get_handler", return_value=mock_handler),
+        patch("macaron.__main__.PolicyReporter", fake_policy_reporter_cls),
+    ):
+        policy_args = argparse.Namespace(
+            database=str(db_file),
+            show_prelude=False,
+            file=None,
+            existing_policy="malware-detection",
+            package_url="pkg:pypi/django",
+        )
+        result = verify_policy(policy_args)
+        assert result == os.EX_OK
+
+
+def test_verify_existing_policy_not_found(tmp_path: Path) -> None:
+    """Requesting a non-existent policy returns usage error."""
+    db_file = tmp_path / "macaron.db"
+    db_file.write_text("")
+    policy_args = argparse.Namespace(
+        database=str(db_file),
+        show_prelude=False,
+        file=None,
+        existing_policy="no-such-policy",
+        package_url="pkg:pypi/django",
+    )
+    result = verify_policy(policy_args)
+    assert result == os.EX_USAGE