Test error msg

Author: SabineHaas

tests/test_wind_farm.py

@@ -163,3 +163,14 @@ def test_aggregation_of_power_curve_with_missing_power_curve(self):
         msg = 'For an aggregated wind farm power curve each wind'
         with pytest.raises(ValueError, match=msg):
             windfarm.assign_power_curve()
+
+    def test_wind_farm_efficiency_with_missing_efficiency(self):
+        """Test WindFarm.assign_power_curve() with missing efficiency while
+        `wake_losses_model` is 'wind_farm_efficiency'."""
+        wind_turbine_fleet = [
+            {'wind_turbine': WindTurbine(**self.test_turbine),
+             'number_of_turbines': 3}]
+        windfarm = WindFarm(wind_turbine_fleet=wind_turbine_fleet)
+        msg = 'If you use `wake_losses_model`'
+        with pytest.raises(ValueError, match=msg):
+            windfarm.assign_power_curve()