Learning factory - what should I change in my unit tests? Is it ok?

GenericFactory.cs

public abstract class CarFactory
{
    public abstract Car CreateSportsCar();
    public abstract Car CreateFamilyCar();
}

public abstract class Car
{
    public abstract string CompareSpeed(Car car);
}

public class MercedesFactory : CarFactory
{
    public override Car CreateSportsCar()
    {
        return new MercedesSportsCar();
    }

    public override Car CreateFamilyCar()
    {
        return new MercedesFamilyCar();
    }
}

public class AudiFactory : CarFactory
{
    public override Car CreateSportsCar()
    {
        return new AudiSportsCar();
    }

    public override Car CreateFamilyCar()
    {
        return new AudiFamilyCar();
    }
}

public class AudiSportsCar : Car
{
    public override string CompareSpeed(Car familyCar)
    {
        return this.GetType().Name + " is faster than " + familyCar.GetType().Name;
    }
}

public class AudiFamilyCar : Car
{
    public override string CompareSpeed(Car sportsCar)
    {
        return this.GetType().Name + " is slower than " + sportsCar.GetType().Name;
    }
}

public class MercedesSportsCar : Car
{
    public override string CompareSpeed(Car familyCar)
    {
        return this.GetType().Name + " is faster than " + familyCar.GetType().Name;
    }
}

public class MercedesFamilyCar : Car
{
    public override string CompareSpeed(Car sportsCar)
    {
        return this.GetType().Name + " is slower than " + sportsCar.GetType().Name;
    }
}

public class Driver
{
    readonly Car sportsCar;
    readonly Car familyCar;

    public Driver(CarFactory carFactory)
    {
        sportsCar = carFactory.CreateSportsCar();
        familyCar = carFactory.CreateFamilyCar();
    }

    public string CompareSpeeds()
    {
        return familyCar.CompareSpeed(sportsCar);
    }
}

public class Tests
{
    [Fact]
    public void ShouldCreateNotNullObjectMercedesFamilyCarFromGenericFactory()
    {
        var car = new MercedesFamilyCar();
        Assert.NotNull(car);
    }
        
    [Fact]
    public void ShouldCompareSpeedOfMercedesSportsAndFamilyCars()
    {
        var factory = new MercedesFactory();
        var driver = new Driver(factory);
        Assert.Equal("MercedesFamilyCar is slower than MercedesSportsCar", driver.CompareSpeeds());
    }

    [Fact]
    public void ShouldCompareSpeedOfAudiSportsAndFamilyCars()
    {
        var factory = new AudiFactory();
        var driver = new Driver(factory);
        Assert.Equal("AudiFamilyCar is slower than AudiSportsCar", driver.CompareSpeeds());
    }
}