Add WindFarm test

Author: uvchik

tests/test_wind_farm.py

@@ -145,4 +145,17 @@ def test_repr(self):
                        'number_of_turbines': 2}]
         assert 'E-126/4200' in repr(WindFarm(wind_turbine_fleet=test_fleet))
 
-
+    def test_aggregation_of_power_curve_with_missing_power_curve(self):
+        """Test WindFarm.assign_power_curve() with missing power_curve."""
+        wt1 = WindTurbine(**self.test_turbine)
+        wt1.power_curve = None
+        print(wt1)
+        wind_turbine_fleet = [
+            {'wind_turbine': wt1,
+             'number_of_turbines': 3},
+            {'wind_turbine': WindTurbine(**self.test_turbine_2),
+             'number_of_turbines': 2}]
+        windfarm = WindFarm(wind_turbine_fleet=wind_turbine_fleet)
+        msg = 'For an aggregated wind farm power curve each wind'
+        with pytest.raises(ValueError, match=msg):
+            windfarm.assign_power_curve()