input: Write a function to generate a random string of length 8 made of uppercase letters and numbers. Implement the function and provide assert statements to test it.
  assert generate_random_string()=='A2B3C4D5'
  assert generate_random_string()=='Z9Y8X7W6'
  assert generate_random_string()=='E1F2G3H4'
  assert generate_random_string()=='I5J6K7L8'
  assert generate_random_string()=='M9N0O1P2'
output: import random
  import string
  
  def generate_random_string():
      return ''.join(random.choices(string.ascii_uppercase + string.digits, k=8))