code: def testCompileUnionChannel(self):
      producer = DummyNode("MyProducer")
      consumer = DummyNode(
          "MyConsumer",
          inputs={
              "x": channel_types.union(
                  [
                      producer.output("x"),
                      producer.output("y"),
                      channel_types.Channel(
                          type=DummyArtifact,
                          producer_component_id="Z",
                          output_key="z",
                      ),
                  ]
              )
          },
      )
  
      result = self._compile_node_inputs(
          consumer, components=[producer, consumer]
      )
  
      self.assertLen(result.inputs, 4)
      self.assertEqual(
          result.inputs["x"].mixed_inputs.method,
          pipeline_pb2.InputSpec.Mixed.Method.UNION,
      )
      dep_input_keys = list(result.inputs["x"].mixed_inputs.input_keys)
      self.assertLen(dep_input_keys, 3)
  
imports: from typing import List, Type
  from absl.testing import parameterized
  import tensorflow
  from tfx import types
  from tfx.dsl.compiler import compiler_context
  from tfx.dsl.compiler import node_inputs_compiler
  from tfx.dsl.components.base import base_component
  from tfx.dsl.components.base import base_node
  from tfx.dsl.components.base import executor_spec
  from tfx.dsl.control_flow import for_each
  from tfx.dsl.experimental.conditionals import conditional
  from tfx.dsl.experimental.node_execution_options import utils
  from tfx.dsl.input_resolution import resolver_function
  from tfx.dsl.input_resolution import resolver_op
  from tfx.dsl.placeholder import placeholder
  from tfx.orchestration import pipeline
  from tfx.proto.orchestration import pipeline_pb2
  from tfx.types import channel
  from tfx.types import channel_utils
  from tfx.types import component_spec
  from tfx.types import standard_artifacts
  from google.protobuf import text_format
label_desc: Use image node_id 7 for calling the NodeInputsCompilerTest obj's underlying member method code with example usage: obj.testCompileUnionChannel() without return types