code: def test_element_of_strings(self, container_type, labelarray_dtype):
      missing = labelarray_dtype.type("not in the array")
  
      class C(Classifier):
          dtype = categorical_dtype
          missing_value = missing
          inputs = ()
          window_length = 0
  
      c = C()
  
      raw = np.asarray(
          [
              ["", "a", "ab", "ba"],
              ["z", "ab", "a", "ab"],
              ["aa", "ab", "", "ab"],
              ["aa", "a", "ba", "ba"],
          ],
          dtype=labelarray_dtype,
      )
      data = LabelArray(raw, missing_value=missing)
  
      choices = [
          container_type(choices)
          for choices in [
              [],
              ["a", ""],
              ["a", "a", "a", "ab", "a"],
              set(data.reverse_categories) - {missing},
              ["random value", "ab"],
              ["_" * i for i in range(30)],
          ]
      ]
  
      def make_expected(choice_set):
          return np.vectorize(choice_set.__contains__, otypes=[bool])(
              raw
          )
  
      terms = {str(i): c.element_of(s) for i, s in enumerate(choices)}
      expected = {
          str(i): make_expected(s) for i, s in enumerate(choices)
      }
  
      self.check_terms(
          terms=terms,
          expected=expected,
          initial_workspace={c: data},
          mask=self.build_mask(self.ones_mask(shape=data.shape)),
      )
  
imports: from functools import reduce
  import operator
  import numpy
  import pandas
  from zipline.lib.labelarray import LabelArray
  from zipline.pipeline import Classifier
  from zipline.pipeline.data.testing import TestingDataSet
  from zipline.pipeline.expression import methods_to_ops
  from zipline.testing import parameter_space
  from zipline.testing.fixtures import ZiplineTestCase
  from zipline.testing.predicates import assert_equal
  from zipline.utils.numpy_utils import categorical_dtype, int64_dtype
  from .base import BaseUSEquityPipelineTestCase
label_desc: Use image node_id 9 for calling the ClassifierTestCase obj's underlying member method code with example usage: obj.test_element_of_strings(container_type, labelarray_dtype) and returns: np