input: Write a function named `double_add` that takes two integers `num1` and `num2` as input, calculates the sum of the two numbers, and then doubles the result. The function should return the final result.
  
  assert double_add(2, 3) == 10
  assert double_add(0, 0) == 0
  assert double_add(-1, 1) == 0
  assert double_add(-2, -2) == -8
  assert double_add(5, 5) == 20
output: def double_add(num1, num2):
      return (num1 + num2) * 2