C# 中如何進行私有(private)函數測試

  public class User
    {
        public string Name;
        public string Id;
   
        private string GetID()
        {
            return Id;
        }
    }
    [TestClass()]
    public class UserTests
    {
        [TestMethod()]
        public void ToStringTest()
        {
            User user= new User();
            user.Id = "10";

            PrivateObject pObj = new PrivateObject(user);
            var ret = (string)pObj.Invoke("GetID", null);
            Assert.AreEqual("10", ret);
        }
    }