code: def verify_forward_fill_df_if_needed(
      cls, candles, periods, expected_df
  ):
      observed_df = forward_fill_df_if_needed(
          transform_candles_to_df(candles), periods
      )
      assert expected_df.equals(observed_df)
  
file_path: catalyst/tests/exchange/test_exchange_utils.py
imports: from catalyst.exchange.utils.exchange_utils import transform_candles_to_df, forward_fill_df_if_needed, get_candles_df
  from catalyst.testing.fixtures import WithLogger, CatalystTestCase
  from datetime import timedelta
  from pandas import Timestamp, DataFrame, concat
  import numpy
label_desc: Use image node_id 2 for calling the TestExchangeUtils obj's underlying member method code with example usage: obj.verify_forward_fill_df_if_needed(cls, candles, periods, expected_df) without return types