Avoid extra mailbox fetch in batch/test mode and add regression test (#691)

Co-authored-by: Sean Whalen <44679+seanthegeek@users.noreply.github.com>

parsedmarc/__init__.py

@@ -2141,14 +2141,17 @@ def get_dmarc_reports_from_mailbox(
         "smtp_tls_reports": smtp_tls_reports,
     }
 
-    if current_time:
-        total_messages = len(
-            connection.fetch_messages(reports_folder, since=current_time)
-        )
+    if not test and not batch_size:
+        if current_time:
+            total_messages = len(
+                connection.fetch_messages(reports_folder, since=current_time)
+            )
+        else:
+            total_messages = len(connection.fetch_messages(reports_folder))
     else:
-        total_messages = len(connection.fetch_messages(reports_folder))
+        total_messages = 0
 
-    if not test and not batch_size and total_messages > 0:
+    if total_messages > 0:
         # Process emails that came in during the last run
         results = get_dmarc_reports_from_mailbox(
             connection=connection,

tests.py

@@ -1314,6 +1314,45 @@ since = 2d
         self.assertEqual(system_exit.exception.code, 1)
         self.assertEqual(mock_watch_inbox.call_args.kwargs.get("since"), "2d")
 
+
+class _DummyMailboxConnection:
+    def __init__(self):
+        self.fetch_calls = []
+
+    def create_folder(self, folder_name):
+        return None
+
+    def fetch_messages(self, reports_folder, **kwargs):
+        self.fetch_calls.append({"reports_folder": reports_folder, **kwargs})
+        return []
+
+    def fetch_message(self, message_id, **kwargs):
+        return ""
+
+    def delete_message(self, message_id):
+        return None
+
+    def move_message(self, message_id, folder_name):
+        return None
+
+    def keepalive(self):
+        return None
+
+    def watch(self, check_callback, check_timeout):
+        return None
+
+
+class TestMailboxPerformance(unittest.TestCase):
+    def testBatchModeAvoidsExtraFullFetch(self):
+        connection = _DummyMailboxConnection()
+        parsedmarc.get_dmarc_reports_from_mailbox(
+            connection=connection,
+            reports_folder="INBOX",
+            test=True,
+            batch_size=10,
+            create_folders=False,
+        )
+        self.assertEqual(len(connection.fetch_calls), 1)
     @patch("parsedmarc.cli.get_dmarc_reports_from_mailbox")
     @patch("parsedmarc.cli.MSGraphConnection")
     def testCliPassesMsGraphCertificateAuthSettings(