test: add unit tests for APRSDClient._checks initialisation (#238 follow-up) (#257)

- test_checks_initialised_to_false: asserts _checks is False right after
  __init__, catching any regression that removes the initialisation
- test_keepalive_check_first_call_no_reset: verifies no AttributeError and
  no spurious reset on the very first keepalive_check() call even when the
  driver is already dead
- test_keepalive_check: remove the manual _checks = False setup that masked
  the original bug; rely on the __init__ value instead

ChangeLog.md

@@ -8,6 +8,8 @@ Generated by [`auto-changelog`](https://github.com/CookPete/auto-changelog).
 
 ##### Bug Fixes
 
+- Add tests for APRSDClient._checks initialisation and first-call keepalive behaviour [`20da2ad`](https://github.com/craigerl/aprsd/commit/20da2ad)
+
 - Fix APRSDClient._checks AttributeError on first keepalive_check() call — initialise to False in __init__ [`52e1346`](https://github.com/craigerl/aprsd/commit/52e1346)
 
 - Fix APRSISDriver.is_configured() always returning True when driver is disabled [`a9ef65f`](https://github.com/craigerl/aprsd/commit/a9ef65f)

tests/client/test_client.py

@@ -347,13 +347,32 @@ class TestAPRSDClient(unittest.TestCase):
         result = client.decode_packet(frame='test')
         self.assertIsNone(result)
 
+    def test_checks_initialised_to_false(self):
+        """_checks must be False right after __init__ — no AttributeError on first keepalive."""
+        client = APRSDClient(auto_connect=False)
+        self.assertFalse(
+            client._checks,
+            '_checks should be initialised to False in __init__',
+        )
+
+    def test_keepalive_check_first_call_no_reset(self):
+        """First keepalive_check() call must never reset regardless of driver state."""
+        client = APRSDClient(auto_connect=False)
+        self.mock_driver._alive = False  # driver is dead, but _checks is False
+
+        with mock.patch.object(client, 'reset') as mock_reset:
+            # Should not raise AttributeError, and should not reset on first call
+            client.keepalive_check()
+            mock_reset.assert_not_called()
+
+        self.assertTrue(client._checks)
+
     def test_keepalive_check(self):
         """Test keepalive_check() method."""
         client = APRSDClient(auto_connect=False)
-        client._checks = False
         self.mock_driver._alive = True
 
-        # First check should not reset
+        # First check should not reset (driver alive, _checks False → no reset)
         with mock.patch.object(client, 'reset') as mock_reset:
             client.keepalive_check()
             self.assertTrue(client._checks)