BUG: timedelta resample idempotency, #12072

Author: jreback

doc/source/whatsnew/v0.18.0.txt

@@ -359,7 +359,7 @@ Resample API
 ^^^^^^^^^^^^
 
 Like the change in the window functions API :ref:`above <whatsnew_0180.enhancements.moments>`, ``.resample(...)`` is changing to have
-a more groupby-like API. (:issue:`11732`).
+a more groupby-like API. (:issue:`11732`, :issue:`12702`).
 
 .. ipython:: python
 

pandas/tseries/tests/test_resample.py

@@ -522,6 +522,15 @@ def test_resample_single_period_timedelta(self):
             '1 day', freq='2s', periods=3))
         assert_series_equal(result, expected)
 
+    def test_resample_timedelta_idempotency(self):
+
+        # GH 12072
+        index = pd.timedelta_range('0', periods=9, freq='10L')
+        series = pd.Series(range(9), index=index)
+        result = series.resample('10L').mean()
+        expected = series
+        assert_series_equal(result, expected)
+
     def test_resample_rounding(self):
         # GH 8371
         # odd results when rounding is needed