code: def test_exponential_backoff():
      assert _exponential_backoff(0, 1.5, 3, 20) == 1.5
      assert _exponential_backoff(1, 1.5, 3, 20) == 4.5
      assert _exponential_backoff(2, 1.5, 3, 20) == 13.5
      assert _exponential_backoff(5, 1.5, 3, 20) == 20
      # avoid overflow
      assert _exponential_backoff(1000, 1.5, 3, 20) == 20
  
imports: from __future__ import annotations
  import pytest
  from tornado.ioloop import IOLoop
  from distributed import LocalCluster, Status
  from distributed.deploy.cluster import Cluster, _exponential_backoff
  from distributed.utils_test import gen_test
label_desc: Use image node_id 1 for calling a global function with example usage: test_exponential_backoff() without return types