input: Write a python function to generate a unique URL by appending a random string of 8 characters to a base URL.
  assert len(generate_unique_url('www.example.com/')) == len('www.example.com/') + 8
  assert generate_unique_url('www.test.com/').startswith('www.test.com/')
  assert generate_unique_url('https://mysite.org/') != generate_unique_url('https://mysite.org/')
output: import random
  import string
  
  def generate_unique_url(base_url):
      random_string = ''.join(random.choices(string.ascii_letters + string.digits, k=8))
      return base_url + random_string