为什么此控制器操作的结果为空？

Question

我正在从头开始一个新项目。目前我正在设计一些元素并尝试尽早实施单元测试。问题是单元测试失败，原因似乎是来自控制器操作的空响应。在 Watch Window 中，actionResult 显示 "Internal error in the expression evaluator" 并且 contentResult 为空。

我该如何解决这个问题？

xunit 2.2.0.3545，最小起订量 4.7.63.0

这里是单元测试（xunit）：

// Used in the unit tests
private List<City> cities = new List<City>
{
 new City { City_Name = "Chicago", City_Code = 1 },
 new City { City_Name = "New York", City_Code = 2 },
 new City { City_Name = "Seattle", City_Code = 3 }
};

[Fact]
public async Task Get_AllCities_PropertiesArePopulated()
{
    // Arrange
    var mockService = new Mock<ICityService>();
    mockService.Setup(x => x.GetCities()).ReturnsAsync(this.cities);

    var controller = new CityController(mockService.Object);

    // Act
    IHttpActionResult actionResult = await controller.GetCities();
    var contentResult = actionResult as OkNegotiatedContentResult<List<City>>;

    foreach (var city in contentResult.Content)
    {
        // doesn't get here due to .Content being null.
    }
}

这是我的控制器：

public class CityController : ApiController
{
    private readonly ICityService cityService;

    public CityController(ICityService svc)
    {
        this.cityService = svc;
    }

    public async Task<IHttpActionResult> GetCities()
    {
        var cities = await this.cityService.GetCities();

        if (!cities.Any())
        {
            return this.BadRequest();
        }

        return this.Ok(cities);
    }
}

服务接口：

public interface ICityService
{
    Task<IEnumerable<City>> GetCities();
}

Answer 1

GetCities return IEnumerable<City>

Task<IEnumerable<City>> GetCities();

但在测试的转换中，您使用 List<City>

将其转换为错误的类型

var contentResult = actionResult as OkNegotiatedContentResult<List<City>>;

什么时候应该使用IEnumerable<City>

var contentResult = actionResult as OkNegotiatedContentResult<IEnumerable<City>>;

为什么此控制器操作的结果为空？

Why is the result from this controller action null?

c#

unit-testing

moq

xunit

asp.net-web-api