fix pytest

Author: charlesdong1991

Diff for: pandas/tests/test_strings.py

@@ -6,7 +6,6 @@
 from numpy.random import randint
 import pytest
 
-import pandas.compat as compat
 
 from pandas import DataFrame, Index, MultiIndex, Series, concat, isna, notna
 import pandas.core.strings as strings
@@ -3215,14 +3214,13 @@ def test_replace_warning_single_character(self, input_array,
         if warn:
             with tm.assert_produces_warning(FutureWarning,
                                             check_stacklevel=False):
-                result = values.str.replace(single_char, replace_char)
+                result = values.str.replace(single_char, replace_char, regex=None)
         else:
             result = values.str.replace(single_char, replace_char)
 
         expected = Series([expect_array])
         tm.assert_series_equal(result, expected)
 
-    @pytest.mark.skipif(compat.PY2, reason='not in python2')
     def test_casefold(self):
         # GH25405
         expected = Series(['ss', NA, 'case', 'ssd'])