TST: Check DatetimeIndex.drop on DST boundary (pandas-dev#22165)

Closes pandas-devgh-18031.

Author: gfyoung

pandas/tests/indexes/datetimes/test_timezones.py

@@ -738,6 +738,28 @@ def test_dti_drop_dont_lose_tz(self):
 
         assert ind.tz is not None
 
+    def test_drop_dst_boundary(self):
+        # see gh-18031
+        tz = "Europe/Brussels"
+        freq = "15min"
+
+        start = pd.Timestamp("201710290100", tz=tz)
+        end = pd.Timestamp("201710290300", tz=tz)
+        index = pd.date_range(start=start, end=end, freq=freq)
+
+        expected = DatetimeIndex(["201710290115", "201710290130",
+                                  "201710290145", "201710290200",
+                                  "201710290215", "201710290230",
+                                  "201710290245", "201710290200",
+                                  "201710290215", "201710290230",
+                                  "201710290245", "201710290300"],
+                                 tz=tz, freq=freq,
+                                 ambiguous=[True, True, True, True,
+                                            True, True, True, False,
+                                            False, False, False, False])
+        result = index.drop(index[0])
+        tm.assert_index_equal(result, expected)
+
     def test_date_range_localize(self):
         rng = date_range('3/11/2012 03:00', periods=15, freq='H',
                          tz='US/Eastern')