code: def test_series_with_no_fixed_frequency_raises_error(self):
      with self.assertRaisesRegex(ValueError, "no set frequency"):
          observed_time_series = pd.Series(
              [1.0, 2.0, 4.0],
              index=pd.to_datetime(
                  ["2014-01-01", "2014-01-02", "2014-01-04"]
              ),
          )
          sts_util.canonicalize_observed_time_series_with_mask(
              observed_time_series
          )
  
imports: from absl.testing import parameterized
  import numpy
  import pandas
  import tensorflow.compat.v1
  import tensorflow.compat.v2
  from tensorflow_probability.python.distributions import mvn_diag
  from tensorflow_probability.python.distributions import mvn_tril
  from tensorflow_probability.python.distributions import normal
  from tensorflow_probability.python.internal import tensorshape_util
  from tensorflow_probability.python.internal import test_util
  from tensorflow_probability.python.sts.components import local_level
  from tensorflow_probability.python.sts.internal import missing_values_util
  from tensorflow_probability.python.sts.internal import util
label_desc: Use image node_id 8 for calling the _UtilityTests obj's underlying member method code with example usage: obj.test_series_with_no_fixed_frequency_raises_error() without return types