input: Write a python function to generate a random string of lowercase letters with length 10.
  assert len(generate_random_string()) == 10
  assert generate_random_string().islower()
  assert isinstance(generate_random_string(), str)
output: import random
  import string
  
  def generate_random_string():
      return ''.join(random.choices(string.ascii_lowercase, k=10))