class_docstr: Test no outputs.
class_docstr_tok: ["Test","no","outputs","."]
code: def test_map(self):
      p = Pipeline.input("a").map("a", (), lambda x: x).output("a")
  
      self.assertEqual(p(1).to_list(), [[1]])
  
imports: import unittest
  from towhee.operator.nop import NOPNodeOperator
  from towhee.operator import PyOperator
  from towhee.runtime.pipeline import Pipeline
  from towhee.runtime.data_queue import Empty
  from towhee.runtime import ops, register
  from towhee.runtime.runtime_pipeline import RuntimePipeline
label_desc: Use image node_id 1 for calling the TestPipelineNoOutputCol obj's underlying member method code with example usage: obj.test_map() without return types