code: def init_class_fixtures(cls):
      # This is a rare case where we actually want to do work **before** we
      # call init_class_fixtures.  We choose our sids for WithAssetFinder
      # based on the events generated by make_event_data.
      cls.raw_events = make_events(add_nulls=True)
      cls.raw_events_no_nulls = cls.raw_events[
          cls.raw_events["event_date"].notnull()
      ]
      cls.next_value_columns = {
          EventDataSet_US.next_datetime: "datetime",
          EventDataSet_US.next_event_date: "event_date",
          EventDataSet_US.next_float: "float",
          EventDataSet_US.next_int: "int",
          EventDataSet_US.next_string: "string",
          EventDataSet_US.next_string_custom_missing: "string",
      }
      cls.previous_value_columns = {
          EventDataSet_US.previous_datetime: "datetime",
          EventDataSet_US.previous_event_date: "event_date",
          EventDataSet_US.previous_float: "float",
          EventDataSet_US.previous_int: "int",
          EventDataSet_US.previous_string: "string",
          EventDataSet_US.previous_string_custom_missing: "string",
      }
      cls.loader = cls.make_loader(
          events=cls.raw_events,
          next_value_columns=cls.next_value_columns,
          previous_value_columns=cls.previous_value_columns,
      )
      cls.ASSET_FINDER_EQUITY_SIDS = list(
          cls.raw_events["sid"].unique()
      )
      cls.ASSET_FINDER_EQUITY_SYMBOLS = [
          "s" + str(n) for n in cls.ASSET_FINDER_EQUITY_SIDS
      ]
      super(EventsLoaderTestCase, cls).init_class_fixtures()
  
      cls.engine = SimplePipelineEngine(
          lambda c: cls.loader,
          asset_finder=cls.asset_finder,
          default_domain=US_EQUITIES,
      )
  
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 1 for calling the EventsLoaderTestCase obj's underlying member method code with example usage: obj.init_class_fixtures(cls) without return types