input: Write a python function to draw a square spiral pattern with the turtle graphics module.
  assert draw_spiral(5) == None
  assert draw_spiral(10) == None
output: def draw_spiral(length):
      import turtle
      t = turtle.Turtle()
      for i in range(50):
          t.forward(length + i * 5)
          t.right(90)
      turtle.done()