input: Write a function to generate a random string of length 6 using lowercase letters from the English alphabet. The function should use Python's `random` and `string` modules to accomplish this task.
  assert random_string(6) in [''.join(random.choice(string.ascii_lowercase) for _ in range(6)) for _ in range(100)]
  assert len(random_string(6)) == 6
output: import random
  import string
  
  def random_string(length):
      return ''.join(random.choice(string.ascii_lowercase) for _ in range(length))