input: Write a function to create a class in Python that stores and processes data in a Car object. The class should have an initialization method to set the make, model, color, and mileage of the car, and should also include methods to accelerate and decelerate the car.
  
  class Car:
      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
  
  assert Car("Toyota", "Corolla", "Red", 5000).make=="Toyota"
  assert Car("Honda", "Civic", "Blue", 10000).model=="Civic"
  assert Car("Ford", "Mustang", "Yellow", 20000).color=="Yellow"
  assert Car("Tesla", "Model S", "Black", 30000).mileage==30000
  assert Car("BMW", "X5", "White", 40000).speed==0
output: class Car:
      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