add import compat

Author: charlesdong1991

Diff for: pandas/tests/test_strings.py

@@ -12,6 +12,7 @@
 from pandas import DataFrame, Index, MultiIndex, Series, concat, isna, notna
 import pandas.core.strings as strings
 import pandas.util.testing as tm
+import pandas.compat as compat
 from pandas.util.testing import assert_index_equal, assert_series_equal