class_docstr: PipelineManager Test
class_docstr_tok: ["PipelineManager","Test"]
code: def test_return_none(self):
      towhee_dag_test = copy.deepcopy(self.dag_dict)
      towhee_dag_test["_output"]["inputs"] = ()
      towhee_dag_test["_output"]["outputs"] = ()
      runtime_pipeline = RuntimePipeline(towhee_dag_test)
      result = runtime_pipeline(1, 2, 3)
      self.assertEqual(result.size, 0)
  
imports: import copy
  import weakref
  import unittest
  from towhee import pipe
  from towhee.operator import PyOperator
  from towhee.tools.data_visualizer import DataVisualizer
  from towhee.tools.profilers import PerformanceProfiler
  from towhee.runtime.runtime_pipeline import RuntimePipeline
  from towhee.runtime.operator_manager import OperatorRegistry
label_desc: Use image node_id 2 for calling the TestPipelineManager obj's underlying member method code with example usage: obj.test_return_none() without return types