code: def testFutureProducesPlaceholder(self):
      chnl = channel.Channel(type=_MyType)
      future = chnl.future()
      self.assertIsInstance(
          future, placeholder.ChannelWrappedPlaceholder
      )
      self.assertIs(future.channel, chnl)
      self.assertIsInstance(future[0], placeholder.Placeholder)
      self.assertIsInstance(future.value, placeholder.Placeholder)
  
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 6 for calling the ChannelTest obj's underlying member method code with example usage: obj.testFutureProducesPlaceholder() without return types