Refactor Dependency Injection

Final.cs

public class CarFactory
{
    public CarFactory() 
      : this(ServiceLocator.Resolve<IEngine>(),
             ServiceLocator.Resolve<IChassis>())
    {
    }

    private CarFactory(IEngine engine, IChassis chassis)
    {
        Engine = engine;
        Chassis = chassis;
    }

    public IEngine Engine { get; private set; } // public for testing and a very very very very very long comment

    public IChassis Chassis { get; private set; } // public for testing

    public ICar ConstructCar()
    {
        return new Car(Engine, Chassis);
    }
}

PureDependencyInjection.cs

public class CarFactory
{
    public CarFactory(IEngine engine, IChassis chassis)
    {
        Engine = engine;
        Chassis = chassis;
    }

    public IEngine Engine { get; private set; } // public for testing

    public IChassis Chassis { get; private set; } // public for testing

    public ICar ConstructCar()
    {
        return new Car(Engine, Chassis);
    }
}

ServiceLocator.cs

public class CarFactory
{
    public ICar ConstructCar()
    {
        return new Car(ServiceLocator.Resolve<IEngine>(),
                       ServiceLocator.Resolve<IChassis>());
    }
}

public static class ServiceLocator
{
    public static T Resolve<T>()
    {
        // Resolve instance from registered service registrations
    }
}

UnitTest.cs

[TestClass]
public class CarFactoryTests
{
    [TestMethod]
    public void ConstructCar()
    {
        // Arrange
        var autoMocker = new AutoMocker();
        autoMocker.Setup<IEngine,string>(x=>x.Type).Returns("V6");
        var testee = autoMocker.CreateInstance<CarFactory>(true);

        // Act
        var result = testee.ConstructCar();

        // Assert
        result.Should().NotBeNull();
        result.Engine.Type.Should().Be("V6");
    } 
}