TestController.cs

using System.Web.Mvc;
using Sitecore.Mvc.Controllers;

namespace MyProjectNamespace.Controllers
{
	public class TestController : SitecoreController
	{
		private readonly IInjectedClass _injectedClass;
		public TestController()
		{
			_injectedClass = Sitecore.Configuration.Factory.CreateObject("guide/InjectedClass", true) as InjectedClass;
		}

		public ActionResult MyAction()
		{
			var val = _injectedClass.TestMethod();

			//Do work with ability to utilize injected class

			return View();
		}
	}
}