input: Write a function to create a class named Car that stores and processes data for a car object. The class should include attributes like make, model, color, and mileage, and methods to accelerate and decelerate the car. 
  class Car:
      def __init__(self, make, model, color, mileage):
          self.make = make
          self.model = make
          self.color = color
          self.mileage = mileage
          self.speed = 0
  
      def accelerate(self, speed_increase):
          self.speed += speed_increase
  
      def decelerate(self, speed_decrease):
          self.speed -= speed_decrease
  
  assert Car("Toyota", "Camry", "Red", 50000).make == "Toyota"
  assert Car("Toyota", "Camry", "Red", 50000).model == "Camry"
  assert Car("Toyota", "Camry", "Red", 50000).color == "Red"
  assert Car("Toyota", "Camry", "Red", 50000).mileage == 50000
  assert Car("Toyota", "Camry", "Red", 50000).speed == 0
  assert Car("Toyota", "Camry", "Red", 50000).accelerate(20) == 20
  assert Car("Toyota", "Camry", "Red", 50000).decelerate(10) == 10
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_increase):
      self.speed += speed_increase
  
  def decelerate(self, speed_decrease):
      self.speed -= speed_decrease
  