class_docstr: Basic test case for `OperatorPool`.
class_docstr_tok: ["Basic","test","case","for","`","OperatorPool","`","."]
code: def test_not_reusable(self):
      self._op_pool.clear()
      hub_op_id = "local/flat_operator"
  
      op1 = self._op_pool.acquire_op(
          self._key, hub_op_id, None, None, "main", False
      )
      op2 = self._op_pool.acquire_op(
          self._key, hub_op_id, None, None, "main", False
      )
      self.assertEqual(len(self._op_pool), 0)
      self._op_pool.release_op(op2)
      self.assertEqual(len(self._op_pool), 0)
  
      self._op_pool.release_op(op1)
      self.assertEqual(len(self._op_pool), 0)
  
file_path: towhee/tests/unittests/runtime/test_operator_pool.py
imports: import unittest
  from towhee.operator import Operator
  from towhee.runtime.operator_manager import OperatorPool
label_desc: Use image node_id 5 for calling the TestOperatorPool obj's underlying member method code with example usage: obj.test_not_reusable() without return types