class_docstr: FlatMap node test.
code: def test_scalar_empty(self):
      node_info = {
          "inputs": (
              "url",
              "num",
          ),
          "outputs": ("vec",),
          "op_info": {
              "type": "lambda",
              "operator": lambda x, y: [str(x) + str(y)],
              "tag": "main",
              "init_args": None,
              "init_kws": {},
          },
          "iter_info": {"type": "flat_map", "param": None},
          "config": {"name": "test"},
          "next_nodes": ["_output"],
      }
      node_repr = NodeRepr(uid="test_node", **node_info)
      in_que = DataQueue(
          [
              ("url", ColumnType.SCALAR),
              ("num", ColumnType.QUEUE),
              ("another", ColumnType.QUEUE),
          ]
      )
      in_que.put(("test_url", 1, 1))
      in_que.put(("test_url", Empty(), 1))
      in_que.seal()
      out_que = DataQueue(
          [
              ("url", ColumnType.SCALAR),
              ("num", ColumnType.QUEUE),
              ("another", ColumnType.QUEUE),
              ("vec", ColumnType.QUEUE),
          ]
      )
      node = create_node(node_repr, self.op_pool, [in_que], [out_que])
      self.assertTrue(node.initialize())
      f = self.thread_pool.submit(node.process)
      f.result()
      self.assertEqual(
          out_que.get_dict(),
          {
              "url": "test_url",
              "num": 1,
              "another": 1,
              "vec": "test_url1",
          },
      )
      self.assertEqual(
          out_que.get_dict(),
          {
              "url": "test_url",
              "num": Empty(),
              "another": 1,
              "vec": Empty(),
          },
      )
  
imports: import unittest
  import time
  import copy
  import uuid
  from concurrent.futures import ThreadPoolExecutor
  from towhee.runtime.node_repr import NodeRepr
  from towhee.runtime.nodes import create_node, NodeStatus
  from towhee.runtime.data_queue import DataQueue, ColumnType, Empty
  from towhee.runtime.operator_manager import OperatorPool
label_desc: Use image node_id 12 for calling the TestFlatMapNode obj's underlying member method code with example usage: obj.test_scalar_empty() without return types