Testing each usage of ?.

example.cs

void Main()
{
    It_should_return_the_name_from_the_person_on_the_invoice_on_the_order();
    It_should_return_nothing_if_the_person_is_not_set();
    It_should_return_nothing_if_the_invoice_is_not_set();
    It_should_return_nothing_if_given_nothing();
}

public static string GetNameFrom(Order order)
{
    return order?.Invoice?.Person?.Name;
}

public static void It_should_return_the_name_from_the_person_on_the_invoice_on_the_order()
{
    var name = Guid.NewGuid().ToString();
    var order = new Order { Invoice = new Invoice { Person = new Person { Name = name } } };

    GetNameFrom(order).ShouldEqual(name);
}

public static void It_should_return_nothing_if_the_person_is_not_set()
{
    var order = new Order { Invoice = new Invoice { Person = null } };

    GetNameFrom(order).ShouldBeNull();
}

public void It_should_return_nothing_if_the_invoice_is_not_set()
{
    var order = new Order { Invoice = null };

    GetNameFrom(order).ShouldBeNull();
}

public void It_should_return_nothing_if_given_nothing()
{
    Order order = null;
    GetNameFrom(order).ShouldBeNull();
}

public class Order
{
    public Invoice Invoice { get; set; }
}

public class Invoice
{
    public Person Person { get; set; }
}

public class Person
{
    public string Name { get; set; }
}