code: def testPlaceholderWithoutKey(self):
      predicate = _TEST_CHANNEL.future()[0].uri == "test_str"
      placeholder_pb = predicate.encode()
      with self.assertRaisesRegex(
          ValueError,
          "Only supports accessing placeholders with a key on KFPv2.",
      ):
          compiler_utils.placeholder_to_cel(placeholder_pb)
  
imports: import os
  from absl.testing import parameterized
  from kfp.pipeline_spec import pipeline_spec_pb2
  import tensorflow
  from tfx.dsl.io import fileio
  from tfx.orchestration import data_types
  from tfx.orchestration.kubeflow.v2 import compiler_utils
  from tfx.types import artifact
  from tfx.types import channel
  from tfx.types import channel_utils
  from tfx.types import standard_artifacts
  from tfx.types.experimental import simple_artifacts
  import yaml
  from google.protobuf import text_format
label_desc: Use image node_id 7 for calling the PlaceholderToCELTest obj's underlying member method code with example usage: obj.testPlaceholderWithoutKey() without return types