code: def testEnsureTopologicalOrder(self):
      a = EmptyComponent(name="a")
      b = EmptyComponent(name="b")
      c = EmptyComponent(name="c")
      a.add_downstream_node(b)
      a.add_downstream_node(c)
      valid_orders = {"abc", "acb"}
      for order in itertools.permutations([a, b, c]):
          if "".join([c.id for c in order]) in valid_orders:
              self.assertTrue(
                  compiler_utils.ensure_topological_order(order)
              )
          else:
              self.assertFalse(
                  compiler_utils.ensure_topological_order(order)
              )
  
imports: import itertools
  import tensorflow
  from tfx import types
  from tfx.components import CsvExampleGen
  from tfx.components import StatisticsGen
  from tfx.dsl.compiler import compiler_utils
  from tfx.dsl.components.base import base_component
  from tfx.dsl.components.base import base_executor
  from tfx.dsl.components.base import executor_spec
  from tfx.dsl.components.common import importer
  from tfx.dsl.components.common import resolver
  from tfx.dsl.input_resolution.strategies import latest_blessed_model_strategy
  from tfx.dsl.placeholder import placeholder
  from tfx.orchestration import pipeline
  from tfx.proto.orchestration import pipeline_pb2
  from tfx.types import standard_artifacts
  from tfx.types.artifact import Artifact
  from tfx.types.artifact import Property
  from tfx.types.artifact import PropertyType
  from tfx.types.channel import Channel
  from tfx.types.channel import OutputChannel
  from tfx.types.channel_utils import external_pipeline_artifact_query
  from google.protobuf import text_format
  from ml_metadata.proto import metadata_store_pb2
label_desc: Use image node_id 6 for calling the CompilerUtilsTest obj's underlying member method code with example usage: obj.testEnsureTopologicalOrder() without return types