public ICommand this[string commandName]
        {
            get
            {
                if (!_commands.ContainsKey(commandName))
                {
                    var command = new MockCommand(commandName);
                    _commands.Add(commandName, command);
                }

                return (ICommand) _commands[commandName];
            }
        }
        public ICommand this[string commandName]
        {
            get
            {
                if (!_commands.ContainsKey(commandName))
                {
                    var command = new MockCommand(commandName);
                    _commands.Add(commandName, command);
                }

                return((ICommand)_commands[commandName]);
            }
        }