From 960fa5446825eb48d91061bf02e412497bc627f7 Mon Sep 17 00:00:00 2001
From: "Sadie L. Bartholomew" <sadie.bartholomew@ncas.ac.uk>
Date: Mon, 13 Oct 2025 22:30:24 +0100
Subject: [PATCH 1/9] Add unittest skips if ncdump not installed where req. by
 test

---
 cf/test/test_read_write.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/cf/test/test_read_write.py b/cf/test/test_read_write.py
index 82e3e919e8..fad3c05e15 100644
--- a/cf/test/test_read_write.py
+++ b/cf/test/test_read_write.py
@@ -642,6 +642,8 @@ def test_read_write_unlimited(self):
         self.assertTrue(domain_axes["domainaxis0"].nc_is_unlimited())
         self.assertTrue(domain_axes["domainaxis2"].nc_is_unlimited())
 
+    @unittest.skipUnless(
+        shutil.which("ncdump"), "ncdump not available - install nco")
     def test_read_CDL(self):
         subprocess.run(
             " ".join(["ncdump", self.filename, ">", tmpfile]),
@@ -703,6 +705,8 @@ def test_read_CDL(self):
         with self.assertRaises(Exception):
             cf.read("test_read_write.py")
 
+    @unittest.skipUnless(
+        shutil.which("ncdump"), "ncdump not available - install nco")
     def test_read_cdl_string(self):
         """Test the cf.read 'cdl_string' keyword."""
         f = cf.read("example_field_0.nc")[0]
@@ -876,6 +880,8 @@ def test_read_url(self):
             f = cf.read(remote)
             self.assertEqual(len(f), 1)
 
+    @unittest.skipUnless(
+        shutil.which("ncdump"), "ncdump not available - install nco")
     def test_read_dataset_type(self):
         """Test the cf.read 'dataset_type' keyword."""
         # netCDF dataset

From 03aef609b0d20ab22e41ba96c91ecbb7676bcb08 Mon Sep 17 00:00:00 2001
From: "Sadie L. Bartholomew" <sadie.bartholomew@ncas.ac.uk>
Date: Mon, 13 Oct 2025 22:48:10 +0100
Subject: [PATCH 2/9] Add unittest skips on lack of pycodestyle or scipy
 availablility

---
 cf/test/test_Data.py       | 3 +++
 cf/test/test_Field.py      | 3 +++
 cf/test/test_read_write.py | 1 +
 cf/test/test_style.py      | 3 +++
 4 files changed, 10 insertions(+)

diff --git a/cf/test/test_Data.py b/cf/test/test_Data.py
index 5918fb79b6..2f9d89449c 100644
--- a/cf/test/test_Data.py
+++ b/cf/test/test_Data.py
@@ -5,6 +5,7 @@
 import io
 import itertools
 import os
+import shutil
 import tempfile
 import unittest
 import warnings
@@ -618,6 +619,8 @@ def test_Data_apply_masking(self):
         self.assertTrue((b == e.array).all())
         self.assertTrue((b.mask == e.mask.array).all())
 
+    @unittest.skipUnless(
+        shutil.which("scipy"), "scipy not available - install it")
     def test_Data_convolution_filter(self):
         """Test the `convolution_filter` Data method."""
         #        raise unittest.SkipTest("GSASL has no PLAIN support")
diff --git a/cf/test/test_Field.py b/cf/test/test_Field.py
index 881ddbb3eb..f7773dc737 100644
--- a/cf/test/test_Field.py
+++ b/cf/test/test_Field.py
@@ -4,6 +4,7 @@
 import itertools
 import os
 import re
+import shutil
 import tempfile
 import unittest
 
@@ -1961,6 +1962,8 @@ def test_Field_autocyclic(self):
     def test_Field_construct_key(self):
         self.f.construct_key("grid_longitude")
 
+    @unittest.skipUnless(
+        shutil.which("scipy"), "scipy not available - install it")
     def test_Field_convolution_filter(self):
         f = cf.read(self.filename1)[0]
 
diff --git a/cf/test/test_read_write.py b/cf/test/test_read_write.py
index fad3c05e15..aaa3d69443 100644
--- a/cf/test/test_read_write.py
+++ b/cf/test/test_read_write.py
@@ -4,6 +4,7 @@
 import inspect
 import os
 import shutil
+import shutil
 import subprocess
 import tempfile
 import unittest
diff --git a/cf/test/test_style.py b/cf/test/test_style.py
index 13ab4b45ec..c3feb430f3 100644
--- a/cf/test/test_style.py
+++ b/cf/test/test_style.py
@@ -1,6 +1,7 @@
 import datetime
 import faulthandler
 import os
+import shutil
 import unittest
 
 import pycodestyle
@@ -31,6 +32,8 @@ def setUp(self):
             for path in non_cf_python_files
         ]
 
+    @unittest.skipUnless(
+        shutil.which("pycodestyle"), "pycodestyle not available - install it")
     def test_pep8_compliance(self):
         pep8_check = pycodestyle.StyleGuide()
 

From 15ddd3f71c240d24ee219920c7e4f1da49e12e0b Mon Sep 17 00:00:00 2001
From: "Sadie L. Bartholomew" <sadie.bartholomew@ncas.ac.uk>
Date: Mon, 13 Oct 2025 23:26:55 +0100
Subject: [PATCH 3/9] Add unittest skips on lack of matplotlib availablility

---
 cf/test/test_Field.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/cf/test/test_Field.py b/cf/test/test_Field.py
index f7773dc737..5bd7b8f1e4 100644
--- a/cf/test/test_Field.py
+++ b/cf/test/test_Field.py
@@ -1153,6 +1153,8 @@ def test_Field_insert_dimension(self):
         with self.assertRaises(ValueError):
             f.insert_dimension(1, "qwerty")
 
+    @unittest.skipUnless(
+        importlib.util.find_spec("matplotlib"), "matplotlib needs installing")
     def test_Field_indices(self):
         f = cf.read(self.filename)[0]
 

From 8a9a8c2d0fdaedc01ec8d1059dbad6d5853239ed Mon Sep 17 00:00:00 2001
From: "Sadie L. Bartholomew" <sadie.bartholomew@ncas.ac.uk>
Date: Tue, 14 Oct 2025 00:40:14 +0100
Subject: [PATCH 4/9] Process import attempts & consolidate messages for
 unittest skips

---
 cf/test/test_Data.py       | 6 ++++--
 cf/test/test_Field.py      | 8 ++++----
 cf/test/test_read_write.py | 6 +++---
 cf/test/test_style.py      | 7 ++++---
 4 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/cf/test/test_Data.py b/cf/test/test_Data.py
index 2f9d89449c..6727032c2a 100644
--- a/cf/test/test_Data.py
+++ b/cf/test/test_Data.py
@@ -2,6 +2,7 @@
 import contextlib
 import datetime
 import faulthandler
+from importlib.util import find_spec
 import io
 import itertools
 import os
@@ -14,7 +15,6 @@
 
 import dask.array as da
 import numpy as np
-from scipy.ndimage import convolve1d
 
 faulthandler.enable()  # to debug seg faults and timeouts
 
@@ -620,9 +620,11 @@ def test_Data_apply_masking(self):
         self.assertTrue((b.mask == e.mask.array).all())
 
     @unittest.skipUnless(
-        shutil.which("scipy"), "scipy not available - install it")
+        find_spec("scipy"), "scipy required but not installed")
     def test_Data_convolution_filter(self):
         """Test the `convolution_filter` Data method."""
+        from scipy.ndimage import convolve1d
+
         #        raise unittest.SkipTest("GSASL has no PLAIN support")
         d = cf.Data(self.ma, units="m", chunks=(2, 4, 5, 3))
 
diff --git a/cf/test/test_Field.py b/cf/test/test_Field.py
index 5bd7b8f1e4..38a13d810b 100644
--- a/cf/test/test_Field.py
+++ b/cf/test/test_Field.py
@@ -1,16 +1,15 @@
 import atexit
 import datetime
 import faulthandler
+from importlib.util import find_spec
 import itertools
 import os
 import re
-import shutil
 import tempfile
 import unittest
 
 import numpy
 import numpy as np
-from scipy.ndimage import convolve1d
 
 faulthandler.enable()  # to debug seg faults and timeouts
 
@@ -1154,7 +1153,7 @@ def test_Field_insert_dimension(self):
             f.insert_dimension(1, "qwerty")
 
     @unittest.skipUnless(
-        importlib.util.find_spec("matplotlib"), "matplotlib needs installing")
+        find_spec("matplotlib"), "matplotlib required but not installed")
     def test_Field_indices(self):
         f = cf.read(self.filename)[0]
 
@@ -1965,8 +1964,9 @@ def test_Field_construct_key(self):
         self.f.construct_key("grid_longitude")
 
     @unittest.skipUnless(
-        shutil.which("scipy"), "scipy not available - install it")
+        find_spec("scipy"), "scipy required but not installed")
     def test_Field_convolution_filter(self):
+        from scipy.ndimage import convolve1d
         f = cf.read(self.filename1)[0]
 
         window = [0.1, 0.15, 0.5, 0.15, 0.1]
diff --git a/cf/test/test_read_write.py b/cf/test/test_read_write.py
index aaa3d69443..2810c335ed 100644
--- a/cf/test/test_read_write.py
+++ b/cf/test/test_read_write.py
@@ -644,7 +644,7 @@ def test_read_write_unlimited(self):
         self.assertTrue(domain_axes["domainaxis2"].nc_is_unlimited())
 
     @unittest.skipUnless(
-        shutil.which("ncdump"), "ncdump not available - install nco")
+        shutil.which("ncdump"), "ncdump required - install nco")
     def test_read_CDL(self):
         subprocess.run(
             " ".join(["ncdump", self.filename, ">", tmpfile]),
@@ -707,7 +707,7 @@ def test_read_CDL(self):
             cf.read("test_read_write.py")
 
     @unittest.skipUnless(
-        shutil.which("ncdump"), "ncdump not available - install nco")
+        shutil.which("ncdump"), "ncdump required - install nco")
     def test_read_cdl_string(self):
         """Test the cf.read 'cdl_string' keyword."""
         f = cf.read("example_field_0.nc")[0]
@@ -882,7 +882,7 @@ def test_read_url(self):
             self.assertEqual(len(f), 1)
 
     @unittest.skipUnless(
-        shutil.which("ncdump"), "ncdump not available - install nco")
+        shutil.which("ncdump"), "ncdump required - install nco")
     def test_read_dataset_type(self):
         """Test the cf.read 'dataset_type' keyword."""
         # netCDF dataset
diff --git a/cf/test/test_style.py b/cf/test/test_style.py
index c3feb430f3..079fb92bf2 100644
--- a/cf/test/test_style.py
+++ b/cf/test/test_style.py
@@ -1,11 +1,10 @@
 import datetime
 import faulthandler
+from importlib.util import find_spec
 import os
 import shutil
 import unittest
 
-import pycodestyle
-
 faulthandler.enable()  # to debug seg faults and timeouts
 
 import cf
@@ -33,8 +32,10 @@ def setUp(self):
         ]
 
     @unittest.skipUnless(
-        shutil.which("pycodestyle"), "pycodestyle not available - install it")
+        find_spec("pycodestyle"), "pycodestyle required but not installed")
     def test_pep8_compliance(self):
+        import pycodestyle
+
         pep8_check = pycodestyle.StyleGuide()
 
         # Directories to skip in the recursive walk of the directory:

From b5dfe4e47c167358624cd32f0eb05c4c3699ca8a Mon Sep 17 00:00:00 2001
From: "Sadie L. Bartholomew" <sadie.bartholomew@ncas.ac.uk>
Date: Tue, 14 Oct 2025 23:59:04 +0100
Subject: [PATCH 5/9] Prevent RuntimeError raised by tests in
 test_RegridOperator

---
 cf/test/test_RegridOperator.py | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/cf/test/test_RegridOperator.py b/cf/test/test_RegridOperator.py
index dae6be8ce8..d7d59d50c0 100644
--- a/cf/test/test_RegridOperator.py
+++ b/cf/test/test_RegridOperator.py
@@ -7,11 +7,31 @@
 import cf
 
 
+# ESMF renamed its Python module to `esmpy` at ESMF version 8.4.0. Allow
+# either for now for backwards compatibility.
+esmpy_imported = False
+try:
+    import esmpy
+
+    esmpy_imported = True
+except ImportError:
+    try:
+        # Take the new name to use in preference to the old one.
+        import ESMF as esmpy
+
+        esmpy_imported = True
+    except ImportError:
+        pass
+
+
 class RegridOperatorTest(unittest.TestCase):
-    src = cf.example_field(0)
-    dst = cf.example_field(1)
-    r = src.regrids(dst, "linear", return_operator=True)
 
+    def setUp(self):
+        src = cf.example_field(0)
+        dst = cf.example_field(1)
+        r = src.regrids(dst, "linear", return_operator=True)
+
+    @unittest.skipUnless(esmpy_imported, "Requires esmpy/ESMF package.")
     def test_RegridOperator_attributes(self):
         self.assertEqual(self.r.coord_sys, "spherical")
         self.assertEqual(self.r.method, "linear")
@@ -39,6 +59,7 @@ def test_RegridOperator_attributes(self):
         self.assertIsNone(self.r.dst_z)
         self.assertFalse(self.r.ln_z)
 
+    @unittest.skipUnless(esmpy_imported, "Requires esmpy/ESMF package.")
     def test_RegridOperator_copy(self):
         self.assertIsInstance(self.r.copy(), self.r.__class__)
 

From 5feee6c78c25809426771d413be626f6181c3ee0 Mon Sep 17 00:00:00 2001
From: "Sadie L. Bartholomew" <sadie.bartholomew@ncas.ac.uk>
Date: Wed, 15 Oct 2025 00:26:43 +0100
Subject: [PATCH 6/9] Move logic requiring esmpy in test_regrid_{featureType,
 mesh}

---
 cf/test/test_regrid_featureType.py | 10 +++++-----
 cf/test/test_regrid_mesh.py        | 10 +++++-----
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/cf/test/test_regrid_featureType.py b/cf/test/test_regrid_featureType.py
index 198b44dd97..3a1967f3d5 100644
--- a/cf/test/test_regrid_featureType.py
+++ b/cf/test/test_regrid_featureType.py
@@ -36,11 +36,6 @@
 atol = 2e-12
 rtol = 0
 
-meshloc = {
-    "face": esmpy.MeshLoc.ELEMENT,
-    "node": esmpy.MeshLoc.NODE,
-}
-
 
 def esmpy_regrid(coord_sys, method, src, dst, **kwargs):
     """Helper function that regrids one dimension of Field data using
@@ -53,6 +48,11 @@ def esmpy_regrid(coord_sys, method, src, dst, **kwargs):
         Regridded numpy masked array.
 
     """
+    meshloc = {
+        "face": esmpy.MeshLoc.ELEMENT,
+        "node": esmpy.MeshLoc.NODE,
+    }
+
     esmpy_regrid = cf.regrid.regrid(
         coord_sys,
         src,
diff --git a/cf/test/test_regrid_mesh.py b/cf/test/test_regrid_mesh.py
index 3095640135..39e29f26fe 100644
--- a/cf/test/test_regrid_mesh.py
+++ b/cf/test/test_regrid_mesh.py
@@ -39,11 +39,6 @@
 atol = 2e-12
 rtol = 0
 
-meshloc = {
-    "face": esmpy.MeshLoc.ELEMENT,
-    "node": esmpy.MeshLoc.NODE,
-}
-
 
 def esmpy_regrid(coord_sys, method, src, dst, **kwargs):
     """Helper function that regrids one dimension of Field data using
@@ -56,6 +51,11 @@ def esmpy_regrid(coord_sys, method, src, dst, **kwargs):
         Regridded numpy masked array.
 
     """
+    meshloc = {
+        "face": esmpy.MeshLoc.ELEMENT,
+        "node": esmpy.MeshLoc.NODE,
+    }
+
     esmpy_regrid = cf.regrid.regrid(
         coord_sys,
         src,

From a5eb69a631f68ea72b5dc3596d793cd05022497c Mon Sep 17 00:00:00 2001
From: "Sadie L. Bartholomew" <sadie.bartholomew@ncas.ac.uk>
Date: Wed, 15 Oct 2025 17:33:14 +0100
Subject: [PATCH 7/9] Revert skips on now-compulsory module SciPy

---
 cf/test/test_Data.py  | 5 +----
 cf/test/test_Field.py | 4 +---
 2 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/cf/test/test_Data.py b/cf/test/test_Data.py
index 6727032c2a..96b2de0dea 100644
--- a/cf/test/test_Data.py
+++ b/cf/test/test_Data.py
@@ -15,6 +15,7 @@
 
 import dask.array as da
 import numpy as np
+from scipy.ndimage import convolve1d
 
 faulthandler.enable()  # to debug seg faults and timeouts
 
@@ -619,12 +620,8 @@ def test_Data_apply_masking(self):
         self.assertTrue((b == e.array).all())
         self.assertTrue((b.mask == e.mask.array).all())
 
-    @unittest.skipUnless(
-        find_spec("scipy"), "scipy required but not installed")
     def test_Data_convolution_filter(self):
         """Test the `convolution_filter` Data method."""
-        from scipy.ndimage import convolve1d
-
         #        raise unittest.SkipTest("GSASL has no PLAIN support")
         d = cf.Data(self.ma, units="m", chunks=(2, 4, 5, 3))
 
diff --git a/cf/test/test_Field.py b/cf/test/test_Field.py
index 38a13d810b..92a72ff8a8 100644
--- a/cf/test/test_Field.py
+++ b/cf/test/test_Field.py
@@ -10,6 +10,7 @@
 
 import numpy
 import numpy as np
+from scipy.ndimage import convolve1d
 
 faulthandler.enable()  # to debug seg faults and timeouts
 
@@ -1963,10 +1964,7 @@ def test_Field_autocyclic(self):
     def test_Field_construct_key(self):
         self.f.construct_key("grid_longitude")
 
-    @unittest.skipUnless(
-        find_spec("scipy"), "scipy required but not installed")
     def test_Field_convolution_filter(self):
-        from scipy.ndimage import convolve1d
         f = cf.read(self.filename1)[0]
 
         window = [0.1, 0.15, 0.5, 0.15, 0.1]

From 55b1ca35187466d91b94b33d9b5133383b38fdfe Mon Sep 17 00:00:00 2001
From: "Sadie L. Bartholomew" <sadie.bartholomew@ncas.ac.uk>
Date: Wed, 15 Oct 2025 17:39:41 +0100
Subject: [PATCH 8/9] Remove now unused imports from tweaks

---
 cf/test/test_Data.py  | 2 --
 cf/test/test_style.py | 1 -
 2 files changed, 3 deletions(-)

diff --git a/cf/test/test_Data.py b/cf/test/test_Data.py
index 96b2de0dea..5918fb79b6 100644
--- a/cf/test/test_Data.py
+++ b/cf/test/test_Data.py
@@ -2,11 +2,9 @@
 import contextlib
 import datetime
 import faulthandler
-from importlib.util import find_spec
 import io
 import itertools
 import os
-import shutil
 import tempfile
 import unittest
 import warnings
diff --git a/cf/test/test_style.py b/cf/test/test_style.py
index 079fb92bf2..907cfd892b 100644
--- a/cf/test/test_style.py
+++ b/cf/test/test_style.py
@@ -2,7 +2,6 @@
 import faulthandler
 from importlib.util import find_spec
 import os
-import shutil
 import unittest
 
 faulthandler.enable()  # to debug seg faults and timeouts

From 7c576cdaaee5aeb4a415bea2db536a9935fb7840 Mon Sep 17 00:00:00 2001
From: "Sadie L. Bartholomew" <sadie.bartholomew@ncas.ac.uk>
Date: Wed, 15 Oct 2025 17:54:49 +0100
Subject: [PATCH 9/9] Fix setUp variable unittest scoping in
 test_RegridOperator

---
 cf/test/test_RegridOperator.py | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/cf/test/test_RegridOperator.py b/cf/test/test_RegridOperator.py
index d7d59d50c0..d92bf9b554 100644
--- a/cf/test/test_RegridOperator.py
+++ b/cf/test/test_RegridOperator.py
@@ -1,5 +1,6 @@
 import datetime
 import faulthandler
+from importlib.util import find_spec
 import unittest
 
 faulthandler.enable()  # to debug seg faults and timeouts
@@ -10,18 +11,10 @@
 # ESMF renamed its Python module to `esmpy` at ESMF version 8.4.0. Allow
 # either for now for backwards compatibility.
 esmpy_imported = False
-try:
-    import esmpy
-
+# Note: here only need esmpy for cf under-the-hood code, not in test
+# directly, so no need to actually import esmpy, just test it is there.
+if find_spec("esmpy") or find_spec("ESMF"):
     esmpy_imported = True
-except ImportError:
-    try:
-        # Take the new name to use in preference to the old one.
-        import ESMF as esmpy
-
-        esmpy_imported = True
-    except ImportError:
-        pass
 
 
 class RegridOperatorTest(unittest.TestCase):
@@ -29,7 +22,7 @@ class RegridOperatorTest(unittest.TestCase):
     def setUp(self):
         src = cf.example_field(0)
         dst = cf.example_field(1)
-        r = src.regrids(dst, "linear", return_operator=True)
+        self.r = src.regrids(dst, "linear", return_operator=True)
 
     @unittest.skipUnless(esmpy_imported, "Requires esmpy/ESMF package.")
     def test_RegridOperator_attributes(self):