code: def test_load_properly_forward_fills(self):
      # Cut the dates in half so we need to forward fill some data which
      # is not in our window. The results should be computed the same as if
      # we had computed across the entire window and then sliced after the
      # computation.
      dates = self.trading_days[len(self.trading_days) // 2 :]
      results = self.engine.run_pipeline(
          Pipeline({c.name: c.latest for c in EventDataSet_US.columns}),
          start_date=dates[0],
          end_date=dates[-1],
      )
  
      for c in EventDataSet_US.columns:
          if c in self.next_value_columns:
              self.check_next_value_results(
                  c,
                  results[c.name].unstack(),
                  dates,
              )
          elif c in self.previous_value_columns:
              self.check_previous_value_results(
                  c,
                  results[c.name].unstack(),
                  dates,
              )
          else:
              raise AssertionError("Unexpected column %s." % c)
  
imports: from datetime import time
  from itertools import product
  from unittest import skipIf
  import blaze
  import numpy
  import pandas
  import pytz
  from zipline.pipeline import Pipeline, SimplePipelineEngine
  from zipline.pipeline.common import EVENT_DATE_FIELD_NAME, TS_FIELD_NAME, SID_FIELD_NAME
  from zipline.pipeline.data import DataSet, Column
  from zipline.pipeline.domain import US_EQUITIES, EquitySessionDomain
  from zipline.pipeline.loaders.events import EventsLoader
  from zipline.pipeline.loaders.blaze.events import BlazeEventsLoader
  from zipline.pipeline.loaders.utils import next_event_indexer, previous_event_indexer
  from zipline.testing import ZiplineTestCase
  from zipline.testing.fixtures import WithAssetFinder, WithTradingSessions
  from zipline.testing.predicates import assert_equal
  from zipline.utils.numpy_utils import categorical_dtype, datetime64ns_dtype, float64_dtype, int64_dtype
  from zipline.utils.pandas_utils import new_pandas, skip_pipeline_new_pandas
label_desc: Use image node_id 4 for calling the EventsLoaderTestCase obj's underlying member method code with example usage: obj.test_load_properly_forward_fills() without return types