code: def test_context_manager(self):
      with io_util.Materializer(tempfile.mkdtemp()) as materializer:
          values = ["abcd", 91, {"x": "y"}]
          with beam.Pipeline() as p:
              _ = p | beam.Create(values) | materializer.writer()
          got_values = []
          for val in materializer.reader():
              got_values.append(val)
      self.assertCountEqual(values, got_values)
      self.assertEmpty(materializer._output_files())
  
file_path: data-validation/tensorflow_data_validation/utils/io_util_test.py
imports: import tempfile
  from absl.testing import absltest
  import apache_beam
  from tensorflow_data_validation.utils import io_util
label_desc: Use image node_id 3 for calling the MaterializerTest obj's underlying member method code with example usage: obj.test_context_manager() without return types