input: Write a function to generate a random string of length 6. Import the required modules `random` and `string`. The function should generate a string consisting of lowercase letters and should be exactly 6 characters long.
  
  assert random_string(6) != random_string(6)
  assert len(random_string(6)) == 6
  assert all(c in string.ascii_lowercase for c in random_string(6))
output: import random
  import string
  
  def random_string(length):
      return ''.join(random.choices(string.ascii_lowercase, k=length))