Question

Here’s the interface:

public interface IFacebookChatClient
{
    Action OnLogin { get; set; }
    bool Login(string apiKey, string accessToken);
    void SendMessage(string message, string receiverId);
    void Close();
}

Here’s a sample usage:

client.Login("...", "...");

client.OnLogin = () =>
{
    client.SendMessage("Testing", "Hello World!");
    client.Close();
}; 

In the unit test, I would like to verify that SendMessage was called with particular values. Is this possible?

Answer 1

This is possible by attaching property behavior to OnLogin property:

var mock = new Mock<IFacebookChatClient>();
// Tell mock to treat OnLogin as regular property
// Second parameter is initial value (doesn't matter in your case)
mock.SetupProperty(m => m.OnLogin, () => { });

// perform test

mock.Verify(m => m.SendMessage("Testing", "Hello World!"));

Normally, attempt to call property getter results in NullReferenceException unless SetupGet was called as part of mock initialization. Problem here is, we don’t want to return fixed value from getter as it is set by tested code. We need property to behave as property, without Moq in the way. And that’s what SetupProperty does – tells Moq that property setter/getter should be left intact.