input: Write a function to generate a unique 6 digit number using the Python `random` module. The function should return a random number between 100000 and 999999.
  def generate_number():
      random_number = random.randint(100000, 999999)
      return random_number
  
  assert generate_number() >= 100000
  assert generate_number() <= 999999
output: def generate_number():
      random_number = random.randint(100000, 999999)
      return random_number