text: import itertools
  from typing import List
  
  import pytest
  
  from httpcore._utils import exponential_backoff
  
  
  @pytest.mark.parametrize(
      "factor, expected",
      [
          (0.1, [0, 0.1, 0.2, 0.4, 0.8]),
          (0.2, [0, 0.2, 0.4, 0.8, 1.6]),
          (0.5, [0, 0.5, 1.0, 2.0, 4.0]),
      ],
  )
  def test_exponential_backoff(factor: float, expected: List[int]) -> None:
      delays = list(itertools.islice(exponential_backoff(factor), 5))
      assert delays == expected
  