code: def _test_trading_days(self):
      self.assertEqual(
          [x.num_trading_days for x in self.metrics.year_periods], [251]
      )
      self.assertEqual(
          [x.num_trading_days for x in self.metrics.month_periods],
          [20, 19, 23, 19, 22, 22, 20, 23, 20, 22, 21, 20],
      )
  
imports: import datetime
  import calendar
  import pandas
  import numpy
  import catalyst.finance.risk
  from catalyst.utils import factory
  from catalyst.finance.trading import SimulationParameters
  from catalyst.testing.fixtures import WithTradingEnvironment, CatalystTestCase
  from catalyst.finance.risk.period import RiskMetricsPeriod
label_desc: Use image node_id 5 for calling the TestRisk obj's underlying member method code with example usage: obj._test_trading_days() without return types