Why does the property I want to mock need to be virtual?

Question

I\'m doing some unit testing, and mocking some properties using Moq.

Now, this is a Controller test (ASP.NET MVC 3). My Controllers

Answer 1

"So....what i did is the only way?"

No not the only way - you are much better off implementing an interface and mocking that. Then your actual methods can be virtual or not as you choose.

Answer 2

Although, all that was said before is true, it's worth to know that the proxy-mocking approach (like the one that moq uses)i s not the only one possible.

Check http://www.typemock.com/ for a comprehensive, solution, that allows you to mock both sealed classes, non-virtual methods etc. Pretty powerful.

Answer 3

Moq and other similar mocking frameworks can only mock interfaces, abstract methods/properties (on abstract classes) or virtual methods/properties on concrete classes.

This is because it generates a proxy that will implement the interface or create a derived class that overrides those overrideable methods in order to intercept calls.

Answer 4

I've created an interface and wrapper class. e.g.

    public interface IWebClient
    {
        string DownloadString(string url);
    }

    public class WebClient : IWebClient
    {
        private readonly System.Net.WebClient _webClient = new System.Net.WebClient();

        public string DownloadString(string url)
        {
            return _webClient.DownloadString(url);
        }
    }

and then in your unit tests just mock out the interface:

        var mockWebClient = new Mock<IWebClient>();

Obviously you may need to include more properties / methods. But does the trick.

Another useful trick for other mocking problems, such as modifying the current date time (I always use UTC date time):

public interface IDateTimeUtcNowProvider
{
    DateTime UtcNow { get; } 
}

public class DateTimeUtcNowProvider : IDateTimeUtcNowProvider
{
    public DateTime UtcNow { get { return DateTime.UtcNow; } }
}

e.g. if you have a service that runs every x minutes you can just mock out the IDateTimeProvider and return a time that is later to check the service ran again... or whatever.