code: def test_collect_to_container_one_element_collections_works(self):
      with test_pipeline.TestPipeline() as p:
          col_x = p | "col_x" >> beam.Create([2])
          col_y = p | "col_y" >> beam.Create(["str"])
          col_z = p | "col_z" >> beam.Create([["str1", "str2"]])
  
          container = composite_funcs.collect_to_container(
              self.backend,
              {"x": col_x, "y": col_y, "z": col_z},
              TestContainer,
              "Collect to container",
          )
  
          beam_util.assert_that(
              container,
              beam_util.equal_to(
                  [TestContainer(x=2, y="str", z=["str1", "str2"])]
              ),
          )
  
imports: import sys
  import unittest
  from dataclasses import dataclass
  from typing import List
  import apache_beam
  import apache_beam.testing.test_pipeline
  import apache_beam.testing.util
  from absl.testing import parameterized
  import pipeline_dp
  from pipeline_dp import pipeline_functions
  from pipeline_dp import pipeline_backend
label_desc: Use image node_id 4 for calling the BeamBackendTest obj's underlying member method code with example usage: obj.test_collect_to_container_one_element_collections_works() without return types