input: Write a function to create a class in Python that stores and processes data in a Car object. The class should include methods to accelerate and decelerate the car, and should have instance variables for make, model, color, and mileage.
  
  class Car:
      def __init__(self, make, model, color, mileage):
          self.make = make
          self.model = model
          self.color = color
          self.mileage = mileage
  
      def accelerate(self, speed):
          self.speed = speed
  
      def decelerate(self, speed):
          self.speed = speed
  
  assert Car("Toyota", "Corolla", "Red", 50000).make == "Toyota"
  assert Car("Honda", "Civic", "Blue", 35000).model == "Civic"
  assert Car("Ford", "Mustang", "Yellow", 40000).color == "Yellow"
  assert Car("Chevrolet", "Malibu", "Black", 60000).mileage == 60000
  car = Car("Tesla", "Model S", "White", 10000)
  car.accelerate(60)
  assert car.speed == 60
  car.decelerate(20)
  assert car.speed == 20
output: def __init__(self, make, model, color, mileage):
      self.make = make
      self.model = model
      self.color = color
      self.mileage = mileage
      self.speed = 0
  
  def accelerate(self, speed):
      self.speed += speed
  
  def decelerate(self, speed):
      self.speed -= speed