code: def testValidUnionChannel(self):
      channel1 = channel.Channel(type=_MyType)
      channel2 = channel.Channel(type=_MyType)
      union_channel = channel.union([channel1, channel2])
      self.assertIs(union_channel.type_name, "MyTypeName")
      self.assertEqual(union_channel.channels, [channel1, channel2])
  
      union_channel = channel.union(
          [channel1, channel.union([channel2])]
      )
      self.assertIs(union_channel.type_name, "MyTypeName")
      self.assertEqual(union_channel.channels, [channel1, channel2])
  
imports: from unittest import mock
  import tensorflow
  from tfx.dsl.input_resolution import resolver_op
  from tfx.dsl.placeholder import placeholder
  from tfx.types import artifact
  from tfx.types import channel
  from tfx.types import resolved_channel
  from google.protobuf import struct_pb2
  from ml_metadata.proto import metadata_store_pb2
label_desc: Use image node_id 7 for calling the ChannelTest obj's underlying member method code with example usage: obj.testValidUnionChannel() without return types