.NET 8 Moq GetRequiredKeyedService Setup错误如何排查解决？

.NET 8 Moq mock GetRequiredKeyedService Setup报错 项目代码里有地方用到IServiceProvider.GetRequiredKeyedService<T>来解析服务，在写单元测试时需要Mock它，本以为像下面这样写就可以了： var serviceProvider = new Mock<IServiceProvider>(); serviceProvider.Setup(x => x.GetRequiredKeyedService<AAA>(It.IsAny<BBB>())).Returns(new CCC()); 没想到报错了: Test method threw exception: System.NotSupportedException: Unsupported expression: x => x.GetRequiredKeyedService(It.IsAny<Type>(), It.IsAny<object>()) Extension methods (here: ServiceProviderKeyedServiceExtensions.GetRequiredKeyedService) may not be used in setup / verification expressions. Stack Trace:  Guard.IsOverridable(MethodInfo method, Expression expression) line 87 MethodExpectation.ctor(LambdaExpression expression, MethodInfo method, IReadOnlyList`1 arguments, Boolean exactGenericTypeArguments, Boolean skipMatcherInitialization, Boolean allowNonOverridable) line 236 ExpressionExtensions.<Split>g__Split|5_0(Expression e, Expression& r, MethodExpectation& p, Boolean assignment, Boolean allowNonOverridableLastProperty) line 256 ExpressionExtensions.Split(LambdaExpression expression, Boolean allowNonOverridableLastProperty) line 170 Mock.SetupRecursive[TSetup](Mock mock, LambdaExpression expression, Func`4 setupLast, Boolean allowNonOverridableLastProperty) line 728 Mock.Setup(Mock mock, LambdaExpression expression, Condition condition) line 562 Mock`1.Setup[TResult](Expression`1 expression) line 645 有点奇怪，难道GetRequiredKeyedService不是接口方法？查看.NET源代码，果然，GetRequiredKeyedService是IServiceProvider的扩展方法，而我们知道Moq是不支持Setup扩展方法的。 /// <summary> /// Get service of type <typeparamref name="T"/> from the <see cref="IServiceProvider"/>. /// </summary> /// <typeparam name="T">The type of service object to get.</typeparam> /// <param name="provider">The <see cref="IServiceProvider"/> to retrieve the service object from.</param> /// <param name="serviceKey">An object that specifies the key of service object to get.</param> /// <returns>A service object of type <typeparamref name="T"/>.</returns> /// <exception cref="System.InvalidOperationException">There is no service of type <typeparamref name="T"/>.</exception> public static T GetRequiredKeyedService<T>(this IServiceProvider provider, object? serviceKey) where T : notnull { ThrowHelper.ThrowIfNull(provider); return (T)provider.GetRequiredKeyedService(typeof(T), serviceKey); } 原因找到就好办了，翻看源码，一步步找到IServiceProvider.GetRequiredKeyedService最终调用的接口方法，然后再mock即可。 首先看下requiredServiceSupportingProvider.GetRequiredKeyedService(serviceType, serviceKey)调的是什么方法 /// <summary> /// IKeyedServiceProvider is a service provider that can be used to retrieve services using a key in addition /// to a type. /// </summary> public interface IKeyedServiceProvider : IServiceProvider { /// <summary> /// Gets the service object of the specified type. /// </summary> /// <param name="serviceType">An object that specifies the type of service object to get.</param> /// <param name="serviceKey">An object that specifies the key of service object to get.</param> /// <returns> A service object of type serviceType. -or- null if there is no service object of type serviceType.</returns> object? GetKeyedService(Type serviceType, object? serviceKey); /// <summary> /// Gets service of type <paramref name="serviceType"/> from the <see cref="IServiceProvider"/> implementing /// this interface. /// </summary> /// <param name="serviceType">An object that specifies the type of service object to get.</param> /// <param name="serviceKey">The <see cref="ServiceDescriptor.ServiceKey"/> of the service.</param> /// <returns>A service object of type <paramref name="serviceType"/>. /// Throws an exception if the <see cref="IServiceProvider"/> cannot create the object.</returns> object GetRequiredKeyedService(Type serviceType, object? serviceKey); } 可以看到IKeyedServiceProvider也是继承了IServiceProvider接口，这就更好办了，我们直接Mock IKeyedServiceProvider再Setup即可，将用到IServiceProvider的地方，换成IKeyedServiceProvider。 代码如下： var serviceProvider = new Mock<IKeyedServiceProvider>(); serviceProvider.Setup(x => x.GetRequiredKeyedService(It.IsAny<AAA>(), It.IsAny<BBB>())).Returns(new CCC()); 运行测试，完美。 总结 解决这个问题并不困难，但是如果.Net不开源，看不到源代码，还是有点头疼。