Prevent RuntimeError raised by tests in test_RegridOperator

Author: sadielbartholomew

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__)