input: Write a function to generate a list of unique random numbers between 1 and 20.
  assert len(set(randomListGenerator())) == 20
  assert all(1 <= num <= 20 for num in randomListGenerator())
  assert len(randomListGenerator()) == 20
output: import random
  
  def randomListGenerator():
      return random.sample(range(1, 21), 20)