Update Field.del_construct unit test to check cyclic() tidy

Author: sadielbartholomew

cf/test/test_Field.py

@@ -2594,7 +2594,19 @@ def test_Field_del_construct(self):
             f.del_construct("measure:area"), cf.CellMeasure
         )
 
-        # TODO test cyclic nature
+        # Test a field with cyclic axes, to ensure the cyclic() set is
+        # updated accordingly if a cyclic axes is the one removed.
+        g = cf.example_field(2)  # this has a cyclic axes 'domainaxis2'
+        # To delete a cyclic axes, must first delete this dimension coordinate
+        # because 'domainaxis2' spans it.
+        self.assertIsInstance(
+            g.del_construct("dimensioncoordinate2"), cf.DimensionCoordinate
+        )
+        self.assertEqual(g.cyclic(), set(("domainaxis2",)))
+        self.assertIsInstance(
+            g.del_construct("domainaxis2"), cf.DomainAxis
+        )
+        self.assertEqual(g.cyclic(), set())
 
     def test_Field_persist(self):
         """Test the `persist` Field method."""