class_docstr: Unit test for Config.
code: def test_callable(self):
      pipe = (
          towhee.pipe.input("a")
          .map("a", "b", CAdd(2))
          .map("b", "c", add)
          .map("a", "d", add)
          .output("a", "b", "c", "d")
      )
      graph = pipe.preload()
      self.assertEqual(
          [v.name for _, v in graph._nodes.items()],
          ["_input", "CAdd-0", "add-1", "add-2", "_output"],
      )
      self.assertEqual(pipe(1).get(), [1, 3, 4, 2])
  
imports: import unittest
  import towhee
  from towhee.runtime import ops, register
label_desc: Use image node_id 12 for calling the TestConfig obj's underlying member method code with example usage: obj.test_callable() without return types