add test_values_with_tz_dtypes related to pandas-dev#14052

With respect to the discussion in pandas-dev#14052, the case ["B","B"] (multiple columns of datetime64[ns, tz] with a common tz) could be improved to return an array with the same dtype as the dataframe

Author: sdementen

pandas/tests/frame/test_dtypes.py

@@ -622,3 +622,26 @@ def test_astype_str(self):
                         'NaT                       NaT' in result)
         self.assertTrue('2 2013-01-03 2013-01-03 00:00:00-05:00 '
                         '2013-01-03 00:00:00+01:00' in result)
+
+    def test_values_with_tz_dtypes(self):
+        df = DataFrame({'A': date_range('20130101', periods=3),
+                    'B': date_range('20130101', periods=3, tz='US/Eastern'),
+                    })
+        for col in [
+            ["A"],
+            ["A", "A"],
+            ["A", "B"],
+            ["B"],
+            ["B", "B"],
+        ]:
+            df_sub = df[col]
+
+            # array has the same dtype as dataframe only and only if
+            # - dataframe has a single column
+            # - or all columns are of type datetime64[ns]
+            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])
+
+            # otherwise, dtype is object
+            else:
+                self.assertTrue(df_sub.values.dtype == object)