add tests and error checking

lib/iris/experimental/ugrid/mesh.py

@@ -1555,6 +1555,8 @@ def coord(
 
         """
         if location is not None:
+            if location not in ["node", "edge", "face"]:
+                raise ValueError(f"Expected location to be one of `node`, `edge` or `face`, got `{location}`")
             include_nodes_new = location == "node"
             include_edges_new = location == "edge"
             include_faces_new = location == "face"
@@ -1661,8 +1663,13 @@ def coords(
         if location is not None:
             if isinstance(location, str):
                 _location = [location]
-            else:
+            elif isinstance(location, Iterable):
                 _location = location
+            else:
+                raise TypeError(f"Expected location to be string or an Iterable, got {type(location)}")
+            for loc in _location:
+                if loc not in ["node", "edge", "face"]:
+                    raise ValueError(f"Expected location to contain only `node`, `edge` or `face`, got `{location}`")
             include_nodes_new = "node" in _location
             include_edges_new = "edge" in _location
             include_faces_new = "face" in _location

lib/iris/tests/unit/experimental/ugrid/mesh/test_Mesh.py

@@ -227,7 +227,25 @@ def test_coord(self):
         func = self.mesh.coord
         exception = CoordinateNotFoundError
         self.assertRaisesRegex(exception, ".*but found 2", func, include_nodes=True)
+        self.assertRaisesRegex(exception, ".*but found 2", func, location="node")
         self.assertRaisesRegex(exception, ".*but found none", func, axis="t")
+        self.assertRaisesRegex(
+            ValueError,
+            "include_edges.*incompatible with.*node",
+            func,
+            location="node",
+            include_edges=True,
+        )
+        self.assertRaisesRegex(
+            ValueError,
+            "include_nodes.*incompatible with.*node",
+            func,
+            location="node",
+            include_nodes=False,
+        )
+        self.assertRaisesRegex(
+            ValueError, "Expected location.*got `foo`", func, location="foo"
+        )
 
     def test_coords(self):
         # General results. Method intended for inheritance.
@@ -238,6 +256,9 @@ def test_coords(self):
             {"long_name": "long_name"},
             {"var_name": "node_lon"},
             {"attributes": {"test": 1}},
+            {"include_nodes": True},
+            {"location": "node"},
+            {"location": ["node", "edge"]},
         )
 
         fake_coord = AuxCoord([0])
@@ -248,6 +269,10 @@ def test_coords(self):
             {"long_name": "foo"},
             {"var_name": "foo"},
             {"attributes": {"test": 2}},
+            {"include_nodes": False},
+            {"include_edges": True},
+            {"location": "face"},
+            {"location": ["face", "edge"]},
         )
 
         func = self.mesh.coords
@@ -256,6 +281,25 @@ def test_coords(self):
         for kwargs in negative_kwargs:
             self.assertNotIn(self.NODE_LON, func(**kwargs))
 
+        func = self.mesh.coords
+        self.assertRaisesRegex(
+            ValueError,
+            "include_edges.*incompatible with.*node",
+            func,
+            location=["node", "face"],
+            include_edges=True,
+        )
+        self.assertRaisesRegex(
+            ValueError,
+            "include_nodes.*incompatible with.*node",
+            func,
+            location=["node", "face"],
+            include_nodes=False,
+        )
+        self.assertRaisesRegex(
+            ValueError, "Expected location.*got.*foo", func, location=["node","foo"]
+        )
+
     def test_coords_elements(self):
         # topology_dimension-specific results. Method intended to be overridden.
         all_expected = {