c# - AutoFixture 是否有一种机制来检查返回任何类型列表的方法是否永远不会返回 null？

Question

我想编写一个测试来检查给定命名空间中的类。如果返回 null，则必须检查返回任何类型列表的类的所有方法。如果是这样，测试必须失败。

类/方法本身也有依赖项(构造函数参数和方法参数)，它们应该被自动模拟。

AutoFixture 是否有一种机制来检查返回任何类型列表的方法永远不会返回 null？

示例类:

public class UserService
{
    private readonly IRemotingFacade _remotingFacade;

    public UserService(IRemotingFacade remotingFacade)
    {
        _remotingFacade = remotingFacade;
    }

    // directly return a list
    public IEnumerable<User> GetUsers()
    {

    }

    // directly return a list, pass method parameters
    public IEnumerable<User> GetUsers(string filter)
    {

    }

    // wrapped list
    public IBusinessResponse<IEnumerable<User>> GetUsers()
    {

    }


    // wrapped list, pass method parameters
    public IBusinessResponse<IEnumerable<User>> GetUsers(string filter)
    {

    }
}

所以请考虑列表可以包装在另一个对象中。

Answer 1

AutoFixture 3.18.0 引入了一个名为 Idioms.FsCheck 的新胶水库使用 FsCheck实现可重用 名为 ReturnValueMustNotBeNullAssertion 的断言。

这个新断言验证(或至少使可能)返回值(查询)的方法不会返回 null。

安装

NuGet 上提供了 Idioms.FsCheck:

PM> Install-Package AutoFixture.Idioms.FsCheck

场景

UserService 使用 IRemotingFacade 的注入(inject)实例并公开两个^[1] 查询:

• 用户[] GetUsers()
• 用户[] GetUsers(int)

场景 #1:IRemotingFacade 的注入(inject)实例返回 null:

[Theory, UnitTestConventions]
public void Scenario1(
    ISpecimenBuilder builder,
    [Frozen]Mock<IRemotingFacade> stub)
{
    stub.Setup(x => x.GetUsers()).Returns((User[])null);

    var sut = from x in new Methods<UserService>() select x.GetUsers();

    var assertion = new ReturnValueMustNotBeNullAssertion(builder);
    Assert.Throws<ReturnValueMustNotBeNullException>(() =>
        assertion.Verify(sut));
}

场景 #2:IRemotingFacade 的注入(inject)实例不返回 null:

[Theory, UnitTestConventions]
public void Scenario2(
    ISpecimenBuilder builder,
    [Frozen]Mock<IRemotingFacade> stub,
    User[] users)
{
    stub.Setup(x => x.GetUsers()).Returns(users);

    var sut = from x in new Methods<UserService>() select x.GetUsers();

    var assertion = new ReturnValueMustNotBeNullAssertion(builder);
    Assert.DoesNotThrow(() => assertion.Verify(sut));
}

场景 3:如果 i 是 -1 GetUsers(int) 返回 null:

[Theory, UnitTestConventions]
public void Scenario3(
    ISpecimenBuilder builder,
    [Frozen]Mock<IRemotingFacade> stub,
    User[] users)
{
    stub.Setup(x => x.GetUsers()).Returns(users);

    var sut = from x in new Methods<UserService>() 
              select x.GetUsers(default(int));

    var assertion = new ReturnValueMustNotBeNullAssertion(builder);
    Assert.Throws<ReturnValueMustNotBeNullException>(
        () => assertion.Verify(sut));
}

备注

If you only have F# 3.1 installed ，您还可以在 app.config 文件中添加程序集绑定(bind)重定向:

<dependentAssembly>
  <assemblyIdentity name="FSharp.Core" 
                    publicKeyToken="b03f5f7f11d50a3a" 
                    culture="neutral" />
  <bindingRedirect oldVersion="0.0.0.0-4.3.1.0" 
                   newVersion="4.3.1.0" />
</dependentAssembly>

UnitTestConventionsAttribute 定义为:

internal class UnitTestConventionsAttribute : AutoDataAttribute
{
    internal UnitTestConventionsAttribute()
        : base(new Fixture().Customize(new AutoMoqCustomization()))
    {
    }
}

反射查询是用 Albedo 执行的.

---

^[1] 对于演示，我简化了 original code如下:

public class User
{
}

public interface IRemotingFacade
{
    User[] GetUsers();
}

public class UserService
{
    private readonly IRemotingFacade remotingFacade;

    public UserService(IRemotingFacade remotingFacade)
    {
        if (remotingFacade == null)
            throw new ArgumentNullException("remotingFacade");

        this.remotingFacade = remotingFacade;
    }

    public User[] GetUsers()
    {
        return this.remotingFacade.GetUsers();
    }

    public User[] GetUsers(int i)
    {
        if (i == -1)
            return null;

        return this.remotingFacade.GetUsers();
    }
}