System.ArgumentException : Invalid callback. Setup on method with 0 parameter(s) cannot invoke callback with different number of parameters (1)

[Saibamen]

In my test I get error described in this issue title:

mockedUserRepository.Setup(r => r.GetAll())
                .Returns(new List<DataAccess.Models.User> { user1, user2 }.AsQueryable);

My code for this Setup:

var userList = userRepository.GetAll().Where(x => users.Contains(x.Id)).ToList();

Moq 4.8.1. When I was using 4.7.145 everything was OK.

[stakx]

Possibly a duplicate of #572. Can you please post a minimal but complete test code that reproduces the problem you're describing?

[Saibamen]

@stakx https://github.com/Saibamen/BriskChat/blob/4fe6d36f68bc25f2cb3367d6950169903cee6a4c/TrollChat.BusinessLogic.Tests/Actions/Room/AddNewPrivateConversationTests.cs#L63

[stakx]

Sorry, but please post minimal but complete (self-contained) repro code here.

[neurohunter]

using System;
using NUnit.Framework;
using Moq;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            var a = new A();
            Console.WriteLine(a.DoTheThing("thing"));
            Console.ReadKey();
        }
    }

    [TestFixture]
    public class AFixture
    {
        [Test]
        public void DoTheThingTest()
        {
            // this test fails with Invalid callback error
            var a = Mock.Of<IA>();
            var aMock = Mock.Get(a);
            aMock.Setup(i => i.DoTheThing(It.IsAny<string>())).Returns<string>(v => "Not A Thing");
        }

        [Test]
        public void DoAThing()
        {
            // This test passes
            var a = Mock.Of<IA>();
            var aMock = Mock.Get(a);
            aMock.Setup(i => i.DoAThing()).Returns<string>(v => "Not A Thing");
        }
    }

    public interface IA
    {
        string DoAThing();
        string DoTheThing(string a);
    }


    public class A : IA
    {
        public string DoAThing()
        {
            return "A Thing Default";
        }

        public string DoTheThing(string a)
        {
            return "The Thing" + a;
        }
    }
}

[stakx]

@neurohunter - Could you perhaps explain what your post above is about?

[neurohunter]

@stakx I found this issue with Invalid callback in Moq in my project, found this issue discussion here and noticed that it was closed because no reproduction scenario is provided. So I've basically appended the scenario that I've used to represent the issue.

[stakx]

@neurohunter, OK thanks! I didn't look above your post, I just saw a block of code without any explanation so I was confused enough already to not even look any further. Sorry for that. 😄

[stakx]

@neurohunter - I'm a bit confused however. The test that you've marked as // This test passes fails, and the one you've marked with // this test fails with Invalid callback error passes. Also, I have no clue what the Main method is supposed to do...?

[neurohunter]

@stakx Yes, you're right, I've added comments later by hand and, apparently, mixed things up.
The correct snippet looks like this:

using System;
using NUnit.Framework;
using Moq;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            var a = new A();
            Console.WriteLine(a.DoTheThing("thing"));
            Console.ReadKey();
        }
    }

    [TestFixture]
    public class AFixture
    {
        [Test]
        public void DoTheThingTest()
        {
            // This test passes
            var a = Mock.Of<IA>();
            var aMock = Mock.Get(a);
            aMock.Setup(i => i.DoTheThing(It.IsAny<string>())).Returns<string>(v => "Not A Thing");
        }

        [Test]
        public void DoAThing()
        {
            
            // this test fails with Invalid callback error
            var a = Mock.Of<IA>();
            var aMock = Mock.Get(a);
            aMock.Setup(i => i.DoAThing()).Returns<string>(v => "Not A Thing");
        }
    }

    public interface IA
    {
        string DoAThing();
        string DoTheThing(string a);
    }


    public class A : IA
    {
        public string DoAThing()
        {
            return "A Thing Default";
        }

        public string DoTheThing(string a)
        {
            return "The Thing" + a;
        }
    }
}

Main method is not supposed to do anything, it's just there.

[stakx]

OK, in that case this is simply caused by the documented change as mentioned in the changelog:

4.8.0-rc1 (2017-12-08)

Changed

• Delegates passed to Returns are validated a little more strictly than before (return type and parameter count must match with method being set up) (@stakx, Validate delegates passed to Returns more strictly #520)

This was requested by #445.