input: Write a function to generate a unique 6 digit number. This function should use the random module to generate a random number between 10000 and 99999, ensuring the number is always 6 digits. If the generated number is unique, the function should return it.
  assert generate_number()==12345
  assert generate_number()==67890
  assert generate_number()==54321
  assert generate_number()==98765
  assert generate_number()==11223
output: import random
  
  def generate_number():
      return random.randint(10000, 99999)