class_docstr: Test Pipeline
class_docstr_tok: ["Test","Pipeline"]
code: def test_filter(self):
      pipe = (
          Pipeline.input("a")
          .filter("a", "b", "a", ops.local.filter_operator(5))
          .output("b")
      )
      res = pipe(5)
      self.assertEqual(res.get(), None)
      res = pipe(7)
      self.assertEqual(res.get(), [7])
  
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 15 for calling the TestPipeline obj's underlying member method code with example usage: obj.test_filter() without return types