code: def split_z(self):
      from metaflow.plugins import InternalTestUnboundedForeachInput
  
      self.z = InternalTestUnboundedForeachInput(self.z)
  
imports: from metaflow_test import MetaflowTest, ExpectationFailed, steps, tag
label_desc: Use image node_id 1 for calling the NestedUnboundedForeachTest obj's underlying member method code with example usage: obj.split_z() without return types