模拟扩展方法会导致System.NotSupportedException [英] Mocking of extension method result in System.NotSupportedException

问题描述

我正在对使用IMemoryCache接口的ClientService进行单元测试:

I'm unit testing a ClientService that uses the IMemoryCache interface:

ClientService.cs:

ClientService.cs:

public string Foo()
{        
    //... code

    _memoryCache.Set("MyKey", "SomeValue", new TimeSpan(0, 0, 60));
}

当我尝试使用以下方法模拟IMemoryCache的Set扩展名时:

When I try to mock the IMemoryCache's Set extension with:

AutoMock mock = AutoMock.GetLoose();

var memoryCacheMock = _mock.Mock<IMemoryCache>();

string value = string.Empty;

// Attempt #1:
memoryCacheMock
     .Setup(x => x.Set<string>(It.IsAny<object>(), It.IsAny<string>(), It.IsAny<TimeSpan>()))
     .Returns("");

// Attempt #2:
memoryCacheMock
    .Setup(x => x.Set(It.IsAny<object>(), It.IsAny<object>(), It.IsAny<TimeSpan>()))
    .Returns(new object());

它抛出以下异常:

System.NotSupportedException:不支持的表达式:x => x.Set(It.IsAny()，It.IsAny()， It.IsAny()) 扩展方法(在这里:CacheExtensions.Set)可能无法在设置/验证前使用

System.NotSupportedException: Unsupported expression: x => x.Set(It.IsAny(), It.IsAny(), It.IsAny()) Extension methods (here: CacheExtensions.Set) may not be used in setup / verification ex

这是名称空间Microsoft.Extensions.Caching.Memory

public static class CacheExtensions
{
   public static TItem Set<TItem>(this IMemoryCache cache, object key, TItem value, TimeSpan absoluteExpirationRelativeToNow);
}

推荐答案

扩展方法实际上是静态方法，不能使用 moq 对其进行模拟.您可以嘲笑的是扩展方法本身使用的方法...

Extension methods are actually static methods and they cannot be mocked using moq. What you could mock are the methods used by the extension method itself...

在您的情况下，Set使用CreateEntry，这是IMemoryCache定义的方法，可能会被嘲笑.尝试这样的事情:

In your case Set uses CreateEntry which is the method defined by IMemoryCache and it could be mocked. Try something like this:

memoryCacheMock
    .Setup(x => x.CreateEntry(It.IsAny<object>()))
    .Returns(Mock.Of<ICacheEntry>);

这篇关于模拟扩展方法会导致System.NotSupportedException的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！