signalモジュールのimport漏れを修正

tests/test_app.py

@@ -1,4 +1,8 @@
 import os
+import signal
+
+import app
+
 import unittest
 from unittest.mock import Mock, patch
 
@@ -152,5 +156,23 @@ class EmailMonitorNotificationTests(unittest.TestCase):
             mark_read.assert_called_once_with("42")
 
 
+class ApplicationStartupTests(unittest.TestCase):
+    @patch.dict(os.environ, {**EMAIL_ENV, "DISCORD_WEBHOOK_URL": "https://discord.example/webhook"}, clear=True)
+    @patch("app.run_http_server")
+    @patch("app.threading.Thread")
+    @patch("app.signal.signal")
+    def test_main_registers_signal_handlers_and_starts_services(
+        self, register_signal, thread_class, run_http_server
+    ):
+        monitor_thread = thread_class.return_value
+
+        app.main()
+
+        registered_signals = [call.args[0] for call in register_signal.call_args_list]
+        self.assertEqual(registered_signals, [signal.SIGINT, signal.SIGTERM])
+        monitor_thread.start.assert_called_once_with()
+        run_http_server.assert_called_once_with()
+
+
 if __name__ == "__main__":
     unittest.main()