Refactor non-idiomatic assertions in test_coord_equality (#6862)

* Refactor non-idiomatic assertions in test_coord_equality

* Clarify usage of explicit comparison operators in test_coord_equality

* Clarify usage of explicit comparison operators in test_coord_equality

* Remove trailing space

---------

Co-authored-by: Martin Yeo <[email protected]>

Author: Hazarean

lib/iris/tests/test_cell.py

@@ -96,6 +96,9 @@ def test_in(self):
         assert c not in [3, c2]
 
     def test_coord_equality(self):
+        # NOTE: These comparisons intentionally use explicit operators to ensure each
+        # rich comparison method (__eq__, __ne__, __lt__, __le__, __gt__, __ge__) is
+        # exercised.
         self.d = iris.coords.Cell(1.9, None)
         assert self.d == 1.9
         assert not self.d == [1.5, 1.9]