Test calls to private methods with moq

Question

I have the following method I need to test with Moq. The problem is that each method called in the switch statement is private, including the PublishMessage at the end. But this method (ProcessMessage) is public. How can I test this so that I can ensure the calls are made depending on the parameter? Note that I'm not testing the private methods, I just want to test the "calls". I'd like to mock these private methods and check if they are called using Setup, but Moq does not support mocking private methods.

public void ProcessMessage(DispenserMessageDataContract dispenserMessage)
    {
        var transOptions = new TransactionOptions { IsolationLevel = IsolationLevel.ReadCommitted };
        using (var scope = new TransactionScope(TransactionScopeOption.RequiresNew, transOptions))
        {
            switch (dispenserMessage.Type)
            {
                case DispenserMessageType.AckNack:
                    UpdateAckNackMessageQueue(dispenserMessage);
                    break;

                case DispenserMessageType.FillRequest:
                    CreateFillRequestMessageQueue(dispenserMessage);
                    break;

                case DispenserMessageType.FillEvent:
                    UpdateFillEventMessageQueue(dispenserMessage);
                    break;

                case DispenserMessageType.RequestInventory:
                    CreateRequestInventoryMessageQueue(dispenserMessage);
                    break;

                case DispenserMessageType.ReceiveInventory:
                    CreateReceiveInventoryMessageQueue(dispenserMessage);
                    break;
            }

            scope.Complete();
        }

        PublishMessage(dispenserMessage);
    }

Answer 1

You will have to change those private methods to atleast protected virtual to mock them and then use mock.Protected to mock them(http://blogs.clariusconsulting.net/kzu/mocking-protected-members-with-moq/). You can't mock private methods.

Moq (and few other frameworks) uses Castle Project's DynamicProxy to generate proxies on the fly at run-time so that members of an object can be intercepted without modifying the code of the class. That interception can only be done on public virtual and protected virtual methods.

See below URL for more information: http://www.castleproject.org/projects/dynamicproxy/

Answer 2

Moq is for mocking properties and methods declared in interfaces and or abstract properties and methods in classes.

The idea behind Moq-testing is that you test the interactions between your class-under-test and the rest of the world (its dependencies). Moq does this by creating a "mocked" implementation of the interface or a derivative of the abstract class with the abstract methods implemented.

Moq cannot override existing implementation like your private methods. This is not how Moq works.

Either you should test "ProcessMessage" with all possible input and expected output or you should refactor your class to delegate the calls to interface methods that you can mock with Moq. Testing private methods is a bad concept anyway. They are kept private for a reason, which is to hide the implementation such that it can change at will.