added AuxCoord test

ESadek-MO · ESadek-MO · commit 929b03bded62 · 2023-11-20T15:17:06.000Z
diff --git a/lib/iris/fileformats/netcdf/loader.py b/lib/iris/fileformats/netcdf/loader.py
@@ -243,10 +243,15 @@ def _get_cf_var_data(cf_var, filename):
                 chunks = cf_var.cf_data.chunking()
                 # In the "contiguous" case, pass chunks=None to 'as_lazy_data'.
                 if chunks == "contiguous":
-                    if CHUNK_CONTROL.mode is ChunkControl.Modes.FROM_FILE:
+                    if (
+                        CHUNK_CONTROL.mode is ChunkControl.Modes.FROM_FILE
+                        and isinstance(
+                            cf_var, iris.fileformats.cf.CFDataVariable
+                        )
+                    ):
                         raise KeyError(
                             f"{cf_var.cf_name} does not contain pre-existing chunk specifications."
-                            f"Instead, you might wish to use CHUNK_CONTROL.set(), or just use default"
+                            f" Instead, you might wish to use CHUNK_CONTROL.set(), or just use default"
                             f" behaviour outside of a context manager. "
                         )
                     # Equivalent to chunks=None, but value required by chunking control
diff --git a/lib/iris/tests/unit/fileformats/netcdf/loader/test__chunk_control.py b/lib/iris/tests/unit/fileformats/netcdf/loader/test__chunk_control.py
@@ -7,10 +7,10 @@
 # Import iris.tests first so that some things can be initialised before
 # importing anything else.
 import iris.tests as tests  # isort:skip
-
 from unittest.mock import ANY, patch
 
 import dask
+import numpy as np
 import pytest
 
 import iris
@@ -34,7 +34,18 @@ def save_cubelist_with_sigma(tmp_filepath):
 
 @pytest.fixture
 def save_cube_with_chunksize(tmp_filepath):
-    iris.save(istk.simple_3d(), tmp_filepath, chunksizes=(1, 3, 4))
+    cube = istk.simple_3d()
+    # adding an aux coord allows us to test that
+    # iris.fileformats.netcdf.loader._get_cf_var_data()
+    # will only throw an error if from_file mode is
+    # True when the entire cube has no specified chunking
+    aux = iris.coords.AuxCoord(
+        points=np.zeros((3, 4)),
+        long_name="random",
+        units="1",
+    )
+    cube.add_aux_coord(aux, [1, 2])
+    iris.save(cube, tmp_filepath, chunksizes=(1, 3, 4))
 
 
 @pytest.fixture(scope="session")
