new_contents: from datetime import datetime as dt
  from mock import create_autospec
  from pandas.util.testing import assert_frame_equal
  
  from arctic.store.bitemporal_store import BitemporalStore
  from tests.util import read_str_as_pandas
  
  
  ts1 = read_str_as_pandas("""           sample_dt | near
                           2012-09-08 17:06:11.040 |  1.0
                           2012-10-08 17:06:11.040 |  2.0
                           2012-10-09 17:06:11.040 |  2.5
                           2012-11-08 17:06:11.040 |  3.0""")
  
  def test_add_observe_dt_index():
      self = create_autospec(BitemporalStore, observe_column='col_a',
                             sample_column='col_b')
      assert_frame_equal(BitemporalStore._add_observe_dt_index(self, ts1, as_of=dt(2001, 1, 1)),
                         read_str_as_pandas("""col_b |      col_a | near
                             2012-09-08 17:06:11.040 | 2001-01-01 |  1.0
                             2012-10-08 17:06:11.040 | 2001-01-01 |  2.0
                             2012-10-09 17:06:11.040 | 2001-01-01 |  2.5
                             2012-11-08 17:06:11.040 | 2001-01-01 |  3.0""", num_index=2))
  
subject: Add unit test