code: def test_volatility(self):
      returns_ = pandas_ta.percent_return(self.close)
      result = pandas_ta.utils.volatility(returns_, returns=True)
      self.assertIsInstance(result, float)
      self.assertGreaterEqual(result, 0)
  
      for tf in [
          "years",
          "months",
          "weeks",
          "days",
          "hours",
          "minutes",
          "seconds",
      ]:
          result = pandas_ta.utils.volatility(self.close, tf)
          with self.subTest(tf=tf):
              self.assertIsInstance(result, float)
              self.assertGreaterEqual(result, 0)
  
imports: from unittest import skip, TestCase
  from pandas import DataFrame
  from .config import sample_data
  from .context import pandas_ta
label_desc: Use image node_id 16 for calling the TestUtilityMetrics obj's underlying member method code with example usage: obj.test_volatility() without return types