input: Write a function to create a random string of a specified length. The function should take an integer as input representing the desired length of the string and return a random string of that length. The string should consist of alphanumeric characters (both uppercase and lowercase letters as well as digits).
  
  def generate_string(string_length):
      random_characters = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'
      random_string = ''.join(random.choices(random_characters, k=string_length))
      return random_string
  
  assert len(generate_string(10)) == 10
  assert len(generate_string(5)) == 5
  assert len(generate_string(0)) == 0
  assert generate_string(15).isalnum() == True
  assert any(char.islower() for char in generate_string(10)) == True
  assert any(char.isupper() for char in generate_string(10)) == True
  assert any(char.isdigit() for char in generate_string(10)) == True
output: def generate_string(string_length):
      random_characters = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'
      random_string = ''.join(random.choices(random_characters, k=string_length))
      return random_string