input: Write a function to create a Car class in Python that stores and processes data such as make, model, color, and mileage. The class should have methods to simulate acceleration and deceleration by updating the speed attribute. 
  
  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", "Camry", "Red", 50000).speed == 0
  assert Car("Honda", "Civic", "Blue", 30000).accelerate(20).speed == 20
  assert Car("Ford", "Mustang", "Black", 70000).accelerate(30).decelerate(10).speed == 20
  assert Car("Tesla", "Model S", "White", 10000).accelerate(50).decelerate(50).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
          return self
  
      def decelerate(self, speed):
          self.speed -= speed
          return self
  