Add Events to NMock

While using View Observer on my last project we needed a way to raise events for unit testing. The best solution turned out to be stubs; however, while we were evaluating options Levi Khatskevitch created a DynamicMockWithEvents class.

DynamicMockWithEvents inherits from NMock's DynamicMock, but it also contains support for raising events from a mock. To raise an event from a mock simply call the RaiseEvent method with the event name and any optional args.

public class DynamicMockWithEvents : DynamicMock
{
 private const string ADD_PREFIX = "add_";
 private const string REMOVE_PREFIX = "remove_";

 private readonly EventHandlerList handlers;
 private readonly Type mockedType;

 public DynamicMockWithEvents(Type type) : base(type)
 {
  handlers = new EventHandlerList();
  mockedType = type;
 }

 public override object Invoke(string methodName, params object[] args)
 {
  if (methodName.StartsWith(ADD_PREFIX))
  {
   handlers.AddHandler(GetKey(methodName, ADD_PREFIX), (Delegate) args[0]);
   return null;
  }
  if (methodName.StartsWith(REMOVE_PREFIX))
  {
   handlers.RemoveHandler(GetKey(methodName, REMOVE_PREFIX), (Delegate) args[0]);
   return null;
  }
  return base.Invoke(methodName, args);
 }

 private static string GetKey(string methodName, string prefix)
 {
  return string.Intern(methodName.Substring(prefix.Length));
 }

 public void RaiseEvent(string eventName, params object[] args)
 {
  Delegate handler = handlers[eventName];
  if (handler == null)
  {
   if (mockedType.GetEvent(eventName) == null)
   {
    throw new MissingMemberException("Event " + eventName + " is not defined");
   }
   else if (Strict)
   {
    throw new ApplicationException("Event " + eventName + " is not handled");
   }
  }
  handler.DynamicInvoke(args);
 }
}