add TODO item

Author: sdementen

pandas/tests/frame/test_dtypes.py

@@ -639,6 +639,9 @@ def test_values_with_tz_dtypes(self):
             # array has the same dtype as dataframe only and only if
             # - dataframe has a single column
             # - or all columns are of type datetime64[ns]
+            
+            # TODO: replace 2nd condition by 'all columns are of type datetime64[ns,same timezone]'
+            # i.e. the test should succeed when replacing the condition be `if len(set(df_sub.dtypes.values))==1:`
             if len(df_sub.dtypes) == 1 or all(df_sub.dtypes.values=="<M8[ns]"):
                 self.assertTrue(df_sub.values.dtype == df_sub.dtypes.values[0])