Add tests for more intelligible errors.

lib/iris/experimental/ugrid/load.py

@@ -490,7 +490,7 @@ def _build_mesh_coords(mesh, cf_var):
         # We should probably issue warnings and recover, but that is too much
         # work.  Raising a more intelligible error is easy to do though.
         msg = (
-            f"mesh data variable {cf_var.name!s} has an invalid "
+            f"mesh data variable {cf_var.name!r} has an invalid "
             f"location={location!r}."
         )
         raise ValueError(msg)

lib/iris/tests/unit/experimental/ugrid/load/test_load_meshes.py

@@ -27,50 +27,58 @@ def tearDownModule():
         rmtree(TMP_DIR)
 
 
-def cdl_to_nc(cdl):
-    cdl_path = str(TMP_DIR / "tst.cdl")
-    nc_path = str(TMP_DIR / f"{uuid4()}.nc")
+def cdl_to_nc(cdl, tmpdir=None):
+    if tmpdir is None:
+        tmpdir = TMP_DIR
+    cdl_path = str(tmpdir / "tst.cdl")
+    nc_path = str(tmpdir / f"{uuid4()}.nc")
     # Use ncgen to convert this into an actual (temporary) netCDF file.
     ncgen_from_cdl(cdl_str=cdl, cdl_path=cdl_path, nc_path=nc_path)
     return nc_path
 
 
-class TestsBasic(tests.IrisTest):
+_TEST_CDL_HEAD = """
+netcdf mesh_test {
+    dimensions:
+        node = 3 ;
+        face = 1 ;
+        vertex = 3 ;
+        levels = 2 ;
+    variables:
+        int mesh ;
+            mesh:cf_role = "mesh_topology" ;
+            mesh:topology_dimension = 2 ;
+            mesh:node_coordinates = "node_x node_y" ;
+            mesh:face_node_connectivity = "face_nodes" ;
+        float node_x(node) ;
+            node_x:standard_name = "longitude" ;
+        float node_y(node) ;
+            node_y:standard_name = "latitude" ;
+        int face_nodes(face, vertex) ;
+            face_nodes:cf_role = "face_node_connectivity" ;
+            face_nodes:start_index = 0 ;
+        int levels(levels) ;
+        float node_data(levels, node) ;
+            node_data:coordinates = "node_x node_y" ;
+            node_data:location = "node" ;
+            node_data:mesh = "mesh" ;
+"""
+
+_TEST_CDL_TAIL = """
+data:
+        mesh = 0;
+        node_x = 0., 2., 1.;
+        node_y = 0., 0., 1.;
+        face_nodes = 0, 1, 2;
+        levels = 1, 2;
+        node_data = 0., 0., 0.;
+    }
+"""
+
+
+class TestLoadErrors(tests.IrisTest):
     def setUp(self):
-        self.ref_cdl = """
-            netcdf mesh_test {
-                dimensions:
-                    node = 3 ;
-                    face = 1 ;
-                    vertex = 3 ;
-                    levels = 2 ;
-                variables:
-                    int mesh ;
-                        mesh:cf_role = "mesh_topology" ;
-                        mesh:topology_dimension = 2 ;
-                        mesh:node_coordinates = "node_x node_y" ;
-                        mesh:face_node_connectivity = "face_nodes" ;
-                    float node_x(node) ;
-                        node_x:standard_name = "longitude" ;
-                    float node_y(node) ;
-                        node_y:standard_name = "latitude" ;
-                    int face_nodes(face, vertex) ;
-                        face_nodes:cf_role = "face_node_connectivity" ;
-                        face_nodes:start_index = 0 ;
-                    int levels(levels) ;
-                    float node_data(levels, node) ;
-                        node_data:coordinates = "node_x node_y" ;
-                        node_data:location = "node" ;
-                        node_data:mesh = "mesh" ;
-                data:
-                    mesh = 0;
-                    node_x = 0., 2., 1.;
-                    node_y = 0., 0., 1.;
-                    face_nodes = 0, 1, 2;
-                    levels = 1, 2;
-                    node_data = 0., 0., 0.;
-                }
-            """
+        self.ref_cdl = _TEST_CDL_HEAD + _TEST_CDL_TAIL
         self.nc_path = cdl_to_nc(self.ref_cdl)
 
     def add_second_mesh(self):

lib/iris/tests/unit/experimental/ugrid/load/test_meshload_checks.py

@@ -0,0 +1,77 @@
+import pytest
+
+import iris
+from iris.experimental.ugrid.load import PARSE_UGRID_ON_LOAD
+
+from .test_load_meshes import (
+    _TEST_CDL_HEAD,
+    _TEST_CDL_TAIL,
+    cdl_to_nc,
+)
+
+
+class TestMeshLoad:
+    def _create_testnc(self, location="node", meshdim="node"):
+        # Add an extra (possibly mal-formed) mesh data to the testfile.
+        if location is None:
+            location_cdl = ""
+        else:
+            location_cdl = f'extra_data:location = "{location}" ;'
+
+        extra_cdl = f"""
+        float extra_data(levels, {meshdim}) ;
+            extra_data:coordinates = "node_x node_y" ;
+            {location_cdl}
+            extra_data:mesh = "mesh" ;
+"""
+        # Insert this into the definitions part of the 'standard' testfile CDL
+        extended_cdl = _TEST_CDL_HEAD + extra_cdl + _TEST_CDL_TAIL
+        testfile_path = cdl_to_nc(extended_cdl, tmpdir=self.tmpdir)
+        return testfile_path
+
+    @pytest.fixture(params=["nolocation", "badlocation", "baddim"])
+    def failnc(self, request, tmp_path_factory):
+        self.param = request.param
+        kwargs = {}
+        if self.param == "nolocation":
+            kwargs["location"] = None
+        elif self.param == "badlocation":
+            kwargs["location"] = "invalid_location"
+        elif self.param == "baddim":
+            kwargs["meshdim"] = "vertex"
+        else:
+            raise ValueError(f"unexpected param: {self.param}")
+
+        self.tmpdir = tmp_path_factory.mktemp("meshload")
+        return self._create_testnc(**kwargs)
+
+    def test_extrameshvar__ok(self, tmp_path_factory):
+        # Check that the default cdl construction loads OK
+        self.tmpdir = tmp_path_factory.mktemp("meshload")
+        testnc = self._create_testnc()
+        with PARSE_UGRID_ON_LOAD.context():
+            iris.load(testnc)
+
+    def test_extrameshvar__fail(self, failnc):
+        # Check that the expected errors are raised in various cases.
+        param = self.param
+        if param == "nolocation":
+            match_msg = (
+                "mesh data variable 'extra_data' has an " "invalid location='<empty>'."
+            )
+        elif param == "badlocation":
+            match_msg = (
+                "mesh data variable 'extra_data' has an "
+                "invalid location='invalid_location'."
+            )
+        elif param == "baddim":
+            match_msg = (
+                "mesh data variable 'extra_data' does not have the node mesh "
+                "dimension 'node', in its dimensions."
+            )
+        else:
+            raise ValueError(f"unexpected param: {param}")
+
+        with PARSE_UGRID_ON_LOAD.context():
+            with pytest.raises(ValueError, match=match_msg):
+                iris.load(failnc)