add missing tm from manual rebase

Author: thoo

pandas/tests/indexes/period/test_construction.py

@@ -3,9 +3,11 @@
 
 import pandas as pd
 import pandas.core.indexes.period as period
-from pandas.compat import lrange, PY3, text_type, lmap
-from pandas import (Period, PeriodIndex, period_range, offsets, date_range,
-                    Series, Index)
+import pandas.util.testing as tm
+from pandas import (
+    Index, Period, PeriodIndex, Series, date_range, offsets, period_range
+)
+from pandas.compat import PY3, lmap, lrange, text_type
 from pandas.core.dtypes.dtypes import PeriodDtype