TST: add tests for GH6274

Author: jreback

doc/source/release.rst

@@ -75,7 +75,7 @@ Bug Fixes
 - Inconsistent tz parsing Timestamp/to_datetime for current year (:issue:`5958`)
 - Indexing bugs with reordered indexes (:issue:`6252`, :issue:`6254`)
 - Bug in ``.xs`` with a Series multiindex (:issue:`6258`, :issue:`5684`)
-- Bug in conversion of a string types to a DatetimeIndex with a specified frequency (:issue:`6273`)
+- Bug in conversion of a string types to a DatetimeIndex with a specified frequency (:issue:`6273`, :issue:`6274`)
 
 pandas 0.13.1
 -------------

pandas/tests/test_index.py

@@ -166,6 +166,11 @@ def test_constructor_from_series(self):
         df['date'] = ['1-1-1990', '2-1-1990', '3-1-1990', '4-1-1990', '5-1-1990']
         result = DatetimeIndex(df['date'], freq='MS')
 
+        # GH 6274
+        # infer freq of same
+        result = pd.infer_freq(df['date'])
+        self.assertEqual(result,'MS')
+
     def test_index_ctor_infer_periodindex(self):
         from pandas import period_range, PeriodIndex
         xp = period_range('2012-1-1', freq='M', periods=3)