added test for resampler in a list grouper with NaT

Author: discort

pandas/tests/test_resample.py

@@ -3175,6 +3175,15 @@ def test_median_duplicate_columns(self):
         expected.columns = result.columns
         assert_frame_equal(result, expected)
 
+    def test_resample_list_grouper_with_nat(self):
+        # GH 14715
+        df = pd.DataFrame({'date': pd.date_range('1/1/2011',
+                                                 periods=365, freq='D')})
+        df.iloc[-1] = pd.NaT
+        result = df.groupby([pd.Grouper(key='date', freq='AS')])
+        expected = {pd.Timestamp('2011-01-01'): pd.Index(list(range(364)))}
+        tm.assert_dict_equal(result.groups, expected)
+
 
 class TestTimeGrouper(object):