input: Write a python function to generate a 5 digit pin using random numbers.
  assert len(generate_pin()) == 5
  assert generate_pin().isdigit()
  assert generate_pin() != generate_pin()  # Likely to be True due to randomness
output: import random
  
  def generate_pin():
      return ''.join([str(random.randint(0, 9)) for _ in range(5)])