接口子类可以自定义实现

环境：net framework 4.5.2

namespace Api {
    public interface A {
        void Test1();
        string Test2();
    }
    public abstract class B : A {
        public virtual void Test1() {
        }
        public virtual string Test2() {
            throw new NotImplementedException();
        }
    }
    public class C : B {
        public override void Test1() {
            base.Test1();
        }
    }
    public class D : B {
        //可以不重写也不会报错
    }
    public class E : B {
        public override string Test2() {
            return base.Test2();
        }
    }
}