class_docstr: Test no outputs.
class_docstr_tok: ["Test","no","outputs","."]
code: def test_flush(self):
      flush_data = 0
  
      @register(name="flush_test")
      class FlushTest(PyOperator):
          def __init__(self, factor):
              self.factor = factor
  
          def __call__(self, x):
              return self.factor + x
  
          def flush(self):
              nonlocal flush_data
              flush_data = 10
  
      p = (
          Pipeline.input("a")
          .map("a", "a", ops.flush_test(10))
          .output("a")
      )
      self.assertEqual(p(1).to_list(), [[11]])
      self.assertEqual(flush_data, 0)
      p.flush()
      self.assertEqual(flush_data, 10)
  
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 5 for calling the TestPipelineNoOutputCol obj's underlying member method code with example usage: obj.test_flush() and returns: unknown