Improve error check for FlorisModel merge function (#1044)

* Add test showing missing error

* Fix error handling

floris/floris_model.py

@@ -1745,9 +1745,16 @@ def reinitialize(self, **_):
 
     @staticmethod
     def merge_floris_models(fmodel_list, reference_wind_height=None):
-        """Merge a list of FlorisModel objects into a single FlorisModel object. Note that it uses
-        the very first object specified in fmodel_list to build upon,
+        """Merge a list of FlorisModel objects into a single FlorisModel object.
+        Note that it uses the first object specified in fmodel_list to build upon,
         so it uses those wake model parameters, air density, and so on.
+        Currently, this function supports merging the following components of the FLORIS inputs:
+            - farm
+                - layout_x
+                - layout_y
+                - turbine_type
+            - flow_field
+                - reference_wind_height
 
         Args:
             fmodel_list (list): Array-like of FlorisModel objects.
@@ -1764,8 +1771,8 @@ def merge_floris_models(fmodel_list, reference_wind_height=None):
                 or general solver settings.
         """
 
-        if not isinstance(fmodel_list[0], FlorisModel):
-            raise ValueError(
+        if not all( type(fm) == FlorisModel for fm in fmodel_list ):
+            raise TypeError(
                 "Incompatible input specified. fmodel_list must be a list of FlorisModel objects."
             )
 

tests/floris_model_integration_test.py

@@ -827,3 +827,30 @@ def test_reference_wind_height_methods(caplog):
             turbine_type=["nrel_5MW", "iea_15MW"]
         )
         fmodel.assign_hub_height_to_ref_height() # Shouldn't allow due to multiple turbine types
+
+def test_merge_floris_models():
+
+    # Check that the merge function extends the data as expected
+    fmodel1 = FlorisModel(configuration=YAML_INPUT)
+    fmodel1.set(
+        layout_x=[0, 1000],
+        layout_y=[0, 0]
+    )
+    fmodel2 = FlorisModel(configuration=YAML_INPUT)
+    fmodel2.set(
+        layout_x=[2000, 3000],
+        layout_y=[0, 0]
+    )
+
+    merged_fmodel = FlorisModel.merge_floris_models([fmodel1, fmodel2])
+    assert merged_fmodel.n_turbines == 4
+
+    # Check that this model will run without error
+    merged_fmodel.run()
+
+    # Verify error handling
+
+    ## Input list with incorrect types
+    fmodel_list = [fmodel1, "not a floris model"]
+    with pytest.raises(TypeError):
+        merged_fmodel = FlorisModel.merge_floris_models(fmodel_list)