input: Write a python function to create a Car object and test its accelerate and brake functions.
  assert car_test().accelerate().speed == 10
  assert car_test().accelerate().accelerate().speed == 20
  assert car_test().accelerate().brakes().speed == 0
output: class Car:
      def __init__(self):
          self.speed = 0
  
      def accelerate(self):
          self.speed += 10
          return self
  
      def brakes(self):
          self.speed = max(0, self.speed - 10)
          return self
  
  def car_test():
      return Car()