Mock Testing a class in C# with Moq

Question

I want to mock the GreetingMessageHandler class in C# with Moq and Nunit in Visual Studio 2019 (version 16.8.4)

public class GreetingMessageHandler : AbstractServerMessageHandler
    {
        public GreetingMessageHandler(AbstractServerMessageHandler next) : base(next)
        {

        }

        public override void InnerHandle(ServerSynchroMessage message)
        {
            IpInformation clientServerIpInformation = JsonConvert.DeserializeObject<IpInformation>(message.payload.body.ToString());
            Collection<IpInformation> servers= message.serverReceiver.GetConnectedServer();

            if (!MessageHandlingHelper.ServerExists(servers, clientServerIpInformation)) {
                message.serverReceiver.ConnectToPeer(clientServerIpInformation);
            }
        }
}

And the Test trying to solve is to test the "InnerHandle" function that should on act run and test it if it runs atleast once. Here is my Code:

            //arrange
            var moqGreeting = new Mock<GreetingMessageHandler>();
            var fakeGreet = new GreetingMessageHandler(null);

            moqGreeting.Setup(x => x.InnerHandle(It.IsAny<ServerSynchroMessage>()));

            // act
            fakeGreet.InnerHandle(null);

            // assert
            moqGreeting.Verify(x => x.InnerHandle(It.IsAny<ServerSynchroMessage>()), Times.AtLeastOnce);

The error message I get for this is this:

Test method UnitTestProject.UnitTest1.GreetingMessageHandlerRun threw exception: Castle.DynamicProxy.InvalidProxyConstructorArgumentsException: Can not instantiate proxy of class: SychroClient.Communications.Server. Could not find a parameterless constructor.

To solve the parameterless constructor problem, I tried to give the functions null values to fake the parameters. But it didn´t work and now I am really desperate to find out why and how to solve this to work.

Answer 1

I figured it out in the end... I had to give the Mock a parameter(null) when creating it like this:

[TestMethod]
        public void GreetingMessageHandlerRun()
        {
            // arrange
            
            var moqGreeting = new Mock<GreetingMessageHandler>(null);
            moqGreeting.Setup(x => x.InnerHandle(It.IsAny<ServerSynchroMessage>()));

            // act
            var fakeGreet = moqGreeting.Object;
            fakeGreet.InnerHandle(null);


            // assert
            moqGreeting.Verify(x => x.InnerHandle(It.IsAny<ServerSynchroMessage>()), Times.AtLeastOnce);
        }