xUnit测试将模型添加到列表失败

我使用xUnit来测试我的项目。我有一个测试，检查user是否已经添加了users的list，如下所示:

private readonly IJsonService _jsonService;
private readonly IUserService _userService;
[Fact]
    public void Add_User_To_User_List()
    {
        //Given
        _userService = new UserService(_jsonService, _guidService);
        _jsonService = Substitute.For<IJsonService>();
        var _fakeUserJsonFile = "Users.json";
        var _fakeNewUser = new User()
        {
            ID = new Guid(),
            FirstName = "Denis",
            LastName = "Menis"
        };
        var _fakeUserList = new List<User>
        {
            new User()
                {
                    ID = new Guid(),
                    FirstName = "Paddy",
                    LastName = "Halle"
                },
            new User()
                {
                    ID = new Guid(),
                    FirstName = "Job",
                    LastName = "Blogs"
                }
        };
        var _fakeUpdatedUserList = new List<User>
        {
            new User()
                {
                    ID = new Guid(),
                    FirstName = "Paddy",
                    LastName = "Halle"
                },
            new User()
                {
                    ID = new Guid(),
                    FirstName = "Job",
                    LastName = "Blogs"
                },
            new User()
                {
                    ID = new Guid(),
                    FirstName = "Denis",
                    LastName = "Menis"
                }
        };
        _jsonService.DeserializeObject<User>(_fakeUserJsonFile).Returns(_fakeUserList);
        _jsonService.SerializeObject(_fakeUserJsonFile, _fakeUpdatedUserList).Returns(true);
        //When
        var result = _userService.AddUser(_fakeNewUser);
        //Then
        Assert.Contains(_fakeNewUser, _fakeUpdatedUserList);
    }

现在我知道代码可以工作，因为我先写了它，但是当我运行测试时，它失败了!下面是我将用户添加到用户列表的代码:

public bool AddUser(User user)
    {
        var userList = GetUsers();
        user.ID = _guidService.NewGuid();
        userList.Add(user);
        var serializeObject = _jsonService.SerializeObject(_fileName, userList);
        return serializeObject;
    }

GetUser方法:

public List<User> GetUsers()
    {
        return _jsonService.DeserializeObject<User>(_fileName).ToList();
    }

Deserialise方法:

private readonly IFileSystem _file;
    private readonly HttpContextBase _httpContext;
    private readonly ILogger _logger;
    public JsonService(IFileSystem file, HttpContextBase httpContext, ILogger logger)
    {
        _file = file;
        _httpContext = httpContext;
        _logger = logger;
    }
    public IEnumerable<T> DeserializeObject<T>(string fileName)
    {
        try
        {
            var relativeFileName = _httpContext.Server.MapPath(fileName);
            var readFile = _file.ReadAllText(relativeFileName);
            var list = JsonConvert.DeserializeObject<List<T>>(readFile);
            return list;
        }
        catch (Exception ex)
        {
            _logger.LogException(ex);
            return null;
        }
    }

文件系统类:

public class FileSystem : IFileSystem
{
    public void WriteAllText(string path, string contents)
    {
        File.WriteAllText(path, contents);
    }
    public string ReadAllText(string path)
    {
        return File.ReadAllText(path);
    }
}

当我运行测试时，AddUser方法中的var serializeObject = _jsonService.SerializeObject(_fileName, userList);每次都返回false。

我认为它这样做是因为即使它是与预期结果相同的数据，在内存中它是对相同数据的不同引用。

谁能帮我这个我想要它返回相同的引用数据。如果我说得不够清楚，我可以再详细说明。由于