c# - MVC4 单元测试 NSubstitute 找不到要返回的调用

Question

我有一个 MVC4 网络应用程序，我现在正在对其进行单元测试。它为数据库部分使用 Entity Framework 。我正在使用 NSubstitute 来模拟数据库。这段代码基本上是从另一个运行良好的站点复制和粘贴的，所以我希望我只是遗漏了一些非常简单的东西。

提前致谢!

SQL 中的应用程序表:

AppID   | ApplicationName
----------------------------
1       | MyCoolApplication
2       | MyOtherApplication

实体创建了应用程序类:

public class Application
{
    public int AppID { get; set; }
    public string ApplicationName { get; set; }
}

单元测试的模拟部分如下所示:

var mockDb = Substitute.For<MyCoolApplicationsEntities>();

var applications = new List<Application>
{
    new Application {AppID = 1, ApplicationName = "MyCoolApplication"},
    new Application {AppID = 2, ApplicationName = "MyOtherApplication"},
};

var mockApplicationSet = Substitute.For<IDbSet<Application>, DbSet<Application>>();
mockApplicationSet.Provider.Returns(applications.AsQueryable().Provider);
mockApplicationSet.Expression.Returns(applications.AsQueryable().Expression);
mockApplicationSet.ElementType.Returns(applications.AsQueryable().ElementType);
mockApplicationSet.GetEnumerator().Returns(applications.AsQueryable().GetEnumerator());

mockApplicationSet.When(q => q.Add(Arg.Any<Application>()))
    .Do(q => applications.Add(q.Arg<Application>()));

mockApplicationSet.When(q => q.Remove(Arg.Any<Application>()))
    .Do(q => applications.Remove(q.Arg<Application>()));


mockDb.Applications.Returns(mockApplicationSet); //This is the line creating the error

完整的错误是:

Test method MyProjectName.Controllers.MyControllerTest.TestOfSectionImTesting threw exception: NSubstitute.Exceptions.CouldNotSetReturnDueToNoLastCallException: Could not find a call to return from.

Make sure you called Returns() after calling your substitute (for example: mySub.SomeMethod().Returns(value)), and that you are not configuring other substitutes within Returns() (for example, avoid this: mySub.SomeMethod().Returns(ConfigOtherSub())).

If you substituted for a class rather than an interface, check that the call to your substitute was on a virtual/abstract member. Return values cannot be configured for non-virtual/non-abstract members.

Correct use:

mySub.SomeMethod().Returns(returnValue);

Potentially problematic use:

mySub.SomeMethod().Returns(ConfigOtherSub());

Instead try:

var returnValue = ConfigOtherSub(); 

mySub.SomeMethod().Returns(returnValue);

但这在我的环境中不起作用，因为应用程序不是一种方法。就像我说的，这在我的另一个站点上运行良好，所以它必须是我缺少的基本内容。我在网上找到的任何内容都对我的特殊情况有帮助。我更新到最新版本的 NSubstitute 并卸载/重新安装，但仍然一无所获。

再次感谢您!

Answer 1

NSubstitute 不能模拟非虚拟成员。 (有 quite a few caveats to substituting for classes 。)

MyCoolApplicationsEntities.Applications 需要是虚拟的，.Returns() 才能工作。