TST: Add test for Flight.get_controller_observed_variables() method

tests/unit/test_flight.py

@@ -250,3 +250,11 @@ def test_export_kml(flight_calisto_robust):
     assert np.allclose(test_flight.latitude[:, 1], lat, atol=1e-3) == True
     assert np.allclose(test_flight.longitude[:, 1], lon, atol=1e-3) == True
     assert np.allclose(test_flight.z[:, 1], z, atol=1e-3) == True
+
+
+def test_get_controller_observed_variables(flight_calisto_air_brakes):
+    """Tests whether the method Flight.get_controller_observed_variables is
+    working as intended."""
+    obs_vars = flight_calisto_air_brakes.get_controller_observed_variables()
+    assert isinstance(obs_vars, list)
+    assert len(obs_vars) == 0