input: Write a function that adds two numbers together and prints the result.
  
  def add(a, b):
      sum = a + b
      print(sum)
  
  add(5, 7)
  assert add(3, 4)
  assert add(0, 0)
  assert add(-1, 2)
  assert add(-3, -5)
output: def add(a, b):
      sum = a + b
      print(sum)