Fix Tello test failure on CI by checking Tello identity instead of flag

Change TelloSource.__init__ to check `Tello is None` instead of
`not TELLO_AVAILABLE`. This resolves a CI-specific failure where
the class-level @patch("src.tello_source.TELLO_AVAILABLE", True)
decorator wasn't consistently applying before the first test method
ran (test_commands_disabled_by_config, alphabetically first).

The new check works naturally with @patch("src.tello_source.Tello")
since the mock replaces Tello with a MagicMock (not None), so the
guard passes without needing a separate TELLO_AVAILABLE patch.

Removed all @patch("src.tello_source.TELLO_AVAILABLE", True)
decorators from tests that already patch Tello. Updated
test_creation_without_djitellopy to patch Tello to None instead.

https://claude.ai/code/session_012XY2M4e4QuJnMcVhA2Zicx

Author: claude

src/tello_source.py

@@ -35,7 +35,7 @@ def __init__(self, config: Config):
         """
         super().__init__()
 
-        if not TELLO_AVAILABLE:
+        if Tello is None:
             raise ImportError(
                 "djitellopy is required for Tello support. Install with: pip install djitellopy"
             )

tests/test_tello_interface.py

@@ -40,7 +40,6 @@ def test_import_without_djitellopy(self):
                 pass  # Expected if djitellopy truly not available
 
 
-@patch("src.tello_source.TELLO_AVAILABLE", True)
 @patch("src.tello_source.Tello")
 class TestTelloSource(unittest.TestCase):
     """Test TelloSource class with mocked Tello."""
@@ -397,7 +396,6 @@ def test_release_while_flying(self, mock_tello_class):
 class TestTelloEdgeCases(unittest.TestCase):
     """Test edge cases for Tello source."""
 
-    @patch("src.tello_source.TELLO_AVAILABLE", True)
     @patch("src.tello_source.Tello")
     def test_read_without_opening(self, mock_tello_class):
         """Test reading before opening connection."""
@@ -411,7 +409,6 @@ def test_read_without_opening(self, mock_tello_class):
         self.assertFalse(success)
         self.assertIsNone(frame)
 
-    @patch("src.tello_source.TELLO_AVAILABLE", True)
     @patch("src.tello_source.Tello")
     def test_commands_without_opening(self, mock_tello_class):
         """Test sending commands before opening."""
@@ -426,7 +423,7 @@ def test_commands_without_opening(self, mock_tello_class):
 
         mock_tello_class.assert_not_called()
 
-    @patch("src.tello_source.TELLO_AVAILABLE", False)
+    @patch("src.tello_source.Tello", None)
     def test_creation_without_djitellopy(self):
         """Test that creation fails gracefully without djitellopy."""
         from src.tello_source import TelloSource
@@ -437,7 +434,6 @@ def test_creation_without_djitellopy(self):
             TelloSource(config)
 
 
-@patch("src.tello_source.TELLO_AVAILABLE", True)
 @patch("src.tello_source.Tello")
 class TestTelloSafetyFeatures(unittest.TestCase):
     """Test safety features for Tello source."""