Parameter count mismatch in a Mocked method call

问题

I have this method:

public void Valida(Validazione.IValidator<MyType> validator)
{
    // do something...
    Validazione.IMapper<MyType> mapper = new MyTypeMapper();
    ValidationResult result = validator.Validate(myTypeObj, mapper, new ValidationConfiguration());
    // ...continue doing something else
}

that I want to unit test, so I would mock (using Moq framework) validator to steer the result of Validate method, so I wrote this unit test:

[TestMethod]
public void Long_test_name_as_best_practice()
{
    // arrange
    MyAggregateRoot aggregateRoot = AggregateRoot.Stub();
    var mockedValidator = new Mock<Validazione.IValidator<MyType>>();

    mockedValidator.Setup(a => a.Validate(
        It.Is<MyType>(x => x.Id == Guid.Parse("3F2504E0-4F89-11D3-9A0C-0305E82C3301")),
        It.IsAny<Validazione.IMapper<MyType>>(), 
        It.IsAny<ValidationConfiguration>()
    )).Returns<Validazione.ValidationResult>(x => x = It.IsAny<Validazione.ValidationResult>());

    // act
    aggregateRoot.Valida(mockedValidator.Object);

    // Assert (now showed for readability sake)
}

It builds, it sounds me pretty correct but in the end I get:

An exception of type 'System.Reflection.TargetParameterCountException' occurred in mscorlib.dll but was not handled in user code Additional information: Parameter count mismatch

I google around but I can't understand the reason. To me seems Ok.

Edit after comment(s)

This is the stack trace of the exception:

   in System.Reflection.RuntimeMethodInfo.InvokeArgumentsCheck(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   in System.Reflection.RuntimeMethodInfo.UnsafeInvoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   in System.Delegate.DynamicInvokeImpl(Object[] args)
   in System.Delegate.DynamicInvoke(Object[] args)
   in Moq.Extensions.InvokePreserveStack(Delegate del, Object[] args)
   in Moq.MethodCallReturn`2.Execute(ICallContext call)
   in Moq.ExecuteCall.HandleIntercept(ICallContext invocation, InterceptorContext ctx, CurrentInterceptContext localctx)
   in Moq.Interceptor.Intercept(ICallContext invocation)
   in Moq.Proxy.CastleProxyFactory.Interceptor.Intercept(IInvocation invocation)
   in Castle.DynamicProxy.AbstractInvocation.Proceed()
   in Castle.Proxies.IValidator`1Proxy.Validate(MyType myTypeObj, IMapper`1 mapper, ValidationConfiguration configuration)
   in MyNamespace.Valida(IValidator`1 validator) in c:\Sviluppo\ProjectName\Main\src\Project.MySubProject.Domain\filename.cs:riga 104
   in MyTestNamespace.Long_test_name_as_best_practice() in c:\Sviluppo\ProjectName\Main\src\Project.SubProject.Domain.Tests\Test_AggregateCommand.cs:riga 103

回答1:

In the Returns clause of this Setup statement:

mockedValidator.Setup(a => a.Validate(
    It.Is<MyType>(x => x.Id == Guid.Parse("3F2504E0-4F89-11D3-9A0C-0305E82C3301")),
    It.IsAny<Validazione.IMapper<MyType>>(), 
    It.IsAny<ValidationConfiguration>()
)).Returns<Validazione.ValidationResult>(x => x = It.IsAny<Validazione.ValidationResult>());

It looks like you don't care what this method returns. But you're giving the Returns statement a Func<ValidationResult.ValidationResult>. This is where your exception is coming from.

This syntax is intended to allow you to compute a return value based on the inputs to the method being setup (here it's Validate), and so you're supposed to pass in a Func with the same arguments as the method being setup. Since your method has 3 arguments and you give Returns a function that takes 1, there's an argument mismatch.

If you want to just return any ValidationResult, do this instead:

.Returns(It.IsAny<Validazione.ValidationResult>())

If you actually do want to compute a ValidationResult based on arguments to Validate, do this:

.Returns<MyType, Validazione.IMapper<MyType>, ValidationConfiguration>
    ((m,t,c) => /* TODO: compute a ValidationResult */ )

来源：https://stackoverflow.com/questions/26906718/parameter-count-mismatch-in-a-mocked-method-call