如何模拟 DataServiceQuery 以进行单元测试?
详细信息如下:想象一个 ASP.NET MVC 应用程序,其中控制器与封装模型存储的 ADO.NET DataService 通信(例如,我们将读取客户列表)。通过对服务的引用,我们得到一个继承自 DataServiceContext 的生成类:
namespace Sample.Services
{
public partial class MyDataContext : global::System.Data.Services.Client.DataServiceContext
{
public MyDataContext(global::System.Uri serviceRoot) : base(serviceRoot) { /* ... */ }
public global::System.Data.Services.Client.DataServiceQuery<Customer> Customers
{
get
{
if((this._Customers==null))
{
this._Customers = base.CreateQuery<Customer>("Customers");
}
return this._Customers;
}
}
/* and many more members */
}
}
控制器可以是:
namespace Sample.Controllers
{
public class CustomerController : Controller
{
private IMyDataContext context;
public CustomerController(IMyDataContext context)
{
this.context=context;
}
public ActionResult Index() { return View(context.Customers); }
}
}
如您所见,我使用了一个接受 IMyDataContext 实例的构造函数,以便我们可以在单元测试中使用模拟:
[TestFixture]
public class TestCustomerController
{
[Test]
public void Test_Index()
{
MockContext mockContext = new MockContext();
CustomerController controller = new CustomerController(mockContext);
var customersToReturn = new List<Customer>
{
new Customer{ Id=1, Name="Fred" },
new Customer{ Id=2, Name="Wilma" }
};
mockContext.CustomersToReturn = customersToReturn;
var result = controller.Index() as ViewResult;
var models = result.ViewData.Model;
//Now we have to compare the Customers in models with those in customersToReturn,
//Maybe by loopping over them?
foreach(Customer c in models) //*** LINE A ***
{
//TODO: compare with the Customer in the same position from customersToreturn
}
}
}
MockContext和MyDataContext需要实现相同的接口IMyDataContext:
namespace Sample.Services
{
public interface IMyDataContext
{
DataServiceQuery<Customer> Customers { get; }
/* and more */
}
}
但是,当我们尝试实现 MockContext 类时,由于 DataServiceQuery 的性质,我们遇到了问题(需要明确的是,我们在 IMyDataContext 接口中使用它只是因为这是我们在自动生成的 MyDataContext 中找到的数据类型我们开始的课程)。如果我们尝试写:
public class MockContext : IMyDataContext
{
public IList<Customer> CustomersToReturn { set; private get; }
public DataServiceQuery<Customer> Customers { get { /* ??? */ } }
}
在Customers getter 中,我们希望实例化一个DataServiceQuery 实例,用CustomersToReturn 中的Customers 填充它,然后返回它。我遇到的问题:
1~ DataServiceQuery 没有公共构造函数;要实例化一个,您应该在 DataServiceContext 上调用 CreateQuery;见MSDN
2~如果我让 MockContext 也从 DataServiceContext 继承,并调用 CreateQuery 来获取要使用的 DataServiceQuery,则服务和查询必须绑定到有效的 URI,并且当我尝试迭代或访问查询中的对象时,它将尝试针对该 URI 执行。换句话说,如果我这样更改 MockContext :
namespace Sample.Tests.Controllers.Mocks
{
public class MockContext : DataServiceContext, IMyDataContext
{
public MockContext() :base(new Uri("http://www.contoso.com")) { }
public IList<Customer> CustomersToReturn { set; private get; }
public DataServiceQuery<Customer> Customers
{
get
{
var query = CreateQuery<Customer>("Customers");
query.Concat(CustomersToReturn.AsEnumerable<Customer>());
return query;
}
}
}
}
然后,在单元测试中,我们在标记为 LINE A 的行上收到错误,因为http://www.contoso.com没有托管我们的服务。即使 LINE A 尝试获取模型中的元素数量,也会触发相同的错误。提前致谢。