MNT: refactor tortured logic in test

Author: ngoldbaum

numpy/_core/tests/test_stringdtype.py

@@ -228,19 +228,16 @@ def test_self_casts(dtype, dtype2, strings):
     if hasattr(dtype, "na_object") and hasattr(dtype2, "na_object"):
         na1 = dtype.na_object
         na2 = dtype2.na_object
-        if na1 is na2:
-            assert_array_equal(arr[:-1], newarr[:-1])
-        else:
-            # comparisons between arrays with distinct NA objects
-            # aren't allowed
-            if ((na1 is pd_NA or na2 is pd_NA or
-                 (na1 != na2 and not ((na1 != na1) and (na2 != na2))))):
-                with pytest.raises(TypeError):
-                    arr[:-1] == newarr[:-1]
-            else:
-                assert_array_equal(arr[:-1], newarr[:-1])
-    else:
-        assert_array_equal(arr[:-1], newarr[:-1])
+        if ((na1 is not na2 and
+             # check for pd_NA first because bool(pd_NA) is an error
+             ((na1 is pd_NA or na2 is pd_NA) or
+              # the second check is a NaN check, spelled this way
+              # to avoid errors from math.isnan and np.isnan
+              (na1 != na2 and not (na1 != na1 and na2 != na2))))):
+            with pytest.raises(TypeError):
+                arr[:-1] == newarr[:-1]
+            return
+    assert_array_equal(arr[:-1], newarr[:-1])
 
 
 @pytest.mark.parametrize(