add GH PR reference

Author: jbrockmendel

pandas/tests/series/test_arithmetic.py

@@ -50,6 +50,7 @@ def test_ser_flex_cmp_return_dtypes_empty(self, opname):
                                        ('foo', 'bar', None),
                                        ('baz', 'baz', 'baz')])
     def test_ser_cmp_result_names(self, names, op):
+        # GH#19524
         # so far only for timedelta, and datetime dtypes
 
         # datetime64 dtype