无法模拟配置。使用Moq的格式化程序

我正在开发一个ASP。NET web API应用程序。我正在对应用程序中的每个组件进行单元测试。我使用Moq单元测试框架来模拟数据。现在我想嘲笑 Configuration.Formatters.JsonFormatter 在我的单元测试中,因为我在单元测试下的操作使用它,如下所示:

public HttpResponseMessage Register(model)
{
    return new HttpResponseMessage
            {
                StatusCode = HttpStatusCode.BadRequest,
                Content = new ObjectContent<List<string>>(errors, Configuration.Formatters.JsonFormatter)
            };
}

我想嘲笑 配置格式化程序。JsonFormatter 在单元测试中,如下所示。

[TestMethod]
public void Register_ReturnErrorsWithBadRequest_IfValidationFails()
{
    PostUserRegistration model = new PostUserRegistration {
        Name = "Wai Yan Hein",
        Email = "waiyanhein@gmail.com",
        Password = ""
    };

    Mock<JsonMediaTypeFormatter> formatterMock = new Mock<JsonMediaTypeFormatter>();
    Mock<MediaTypeFormatterCollection> formatterCollection = new Mock<MediaTypeFormatterCollection>();
    formatterCollection.Setup(x => x.JsonFormatter).Returns(formatterMock.Object);
    Mock<HttpConfiguration> httpConfigMock = new Mock<HttpConfiguration>();
    httpConfigMock.Setup(x => x.Formatters).Returns(formatterCollection.Object);
    Mock<IAccountRepo> accRepoMock = new Mock<IAccountRepo>();

    AccountsController controller = new AccountsController(accRepoMock.Object);

    controller.Configuration = httpConfigMock.Object;
    controller.ModelState.AddModelError("", "Faking some model error");
    HttpResponseMessage response = controller.Register(model);
    Assert.AreEqual(response.StatusCode, System.Net.HttpStatusCode.BadRequest);
}

当我运行单元测试时,它给了我这个错误。

系统NotSupportedException:非虚拟服务器上的设置无效 (在VB中可重写)成员:x=>x、 JsonFormatter

那么,我如何修复该错误,以及如何模拟 配置格式化程序。JsonFormatter ?