From 4e869e0fa1a33bb4ff220e534ce1075480070605 Mon Sep 17 00:00:00 2001
From: Lukas Kluft <lukas.kluft@gmail.com>
Date: Sat, 7 Feb 2026 08:12:39 +0100
Subject: [PATCH 1/3] Make CRS in tests non-dimensional

---
 tests/test_healpix_coords.py | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/tests/test_healpix_coords.py b/tests/test_healpix_coords.py
index 432a8a7..ed77304 100644
--- a/tests/test_healpix_coords.py
+++ b/tests/test_healpix_coords.py
@@ -25,10 +25,9 @@ def raw_ds(request):
 
     return xr.Dataset(
         coords={
-            crs_name: (
-                ("crs",),
-                [0],
-                {
+            crs_name: xr.DataArray(
+                name=crs_name,
+                attrs={
                     "grid_mapping_name": "healpix",
                     **map_parameters,
                 },

From 9b7b40af7fcd3c9eea8c796b765ff7cf380f584e Mon Sep 17 00:00:00 2001
From: Lukas Kluft <lukas.kluft@gmail.com>
Date: Sat, 7 Feb 2026 08:16:42 +0100
Subject: [PATCH 2/3] Test refinement level inspection on data arrays

---
 tests/test_healpix_coords.py | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/tests/test_healpix_coords.py b/tests/test_healpix_coords.py
index ed77304..df495a0 100644
--- a/tests/test_healpix_coords.py
+++ b/tests/test_healpix_coords.py
@@ -36,6 +36,16 @@ def raw_ds(request):
     )
 
 
+@pytest.fixture
+def ds(raw_ds):
+    ds = raw_ds.assign_coords(
+        cell=(("cell",), np.arange(12), {"standard_name": "healpix_index"})
+    )
+    ds = ds.assign(variable=(("cell",), np.ones(12), {"grid_mapping": "healpix"}))
+
+    return ds
+
+
 def test_attach_coords_fixes_crs(raw_ds):
     ds = attach_coords(raw_ds)
 
@@ -75,6 +85,16 @@ def test_get_nside(raw_ds):
     assert get_nside(np.arange(12)) == 1
 
 
+def test_get_nside_dataarray(ds):
+    da = ds["variable"]
+
+    # Should work with...
+    assert get_nside(da) == 1
+
+    # .. and without CRS on data arrays
+    assert get_nside(da.drop_vars(da.cf["grid_mapping"].name)) == 1
+
+
 def test_get_nest(raw_ds):
     assert get_nest(raw_ds)
 

From b07e1073e0dba988768e2f496a0ba47cc2a68732 Mon Sep 17 00:00:00 2001
From: Lukas Kluft <lukas.kluft@gmail.com>
Date: Sat, 7 Feb 2026 08:46:02 +0100
Subject: [PATCH 3/3] Fix `get_nside()` for data arrays without CRS

---
 easygems/healpix/__init__.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/easygems/healpix/__init__.py b/easygems/healpix/__init__.py
index 919775b..9d6ddab 100644
--- a/easygems/healpix/__init__.py
+++ b/easygems/healpix/__init__.py
@@ -25,7 +25,8 @@ def get_nest(dx):
 def get_nside(dx):
     try:
         grid_mapping = dx.cf["grid_mapping"]
-    except AttributeError:
+    except (KeyError, AttributeError):
+        # Catch no CF (KeyError) and no grid mapping (AttributeError)
         if dx.squeeze().ndim > 1:
             raise ValueError(
                 "Cannot infer the HEALPix resolution from a multidimensional dataset.\n"