public ExecuteTests()
        {
            _executor = Substitute.For <IMainThreadExecutor>();
            _executor.When(x => x.BeginOnUIThread(Arg.Any <Action>())).Do(x => ((Action)x[0]).Invoke());
            _executor.When(x => x.OnUIThreadAsync(Arg.Any <Action>())).Do(x => ((Action)x[0]).Invoke());
            _executor.When(x => x.OnUIThread(Arg.Any <Action>())).Do(x => ((Action)x[0]).Invoke());

            _action = Substitute.For <Action>();

            Execute.Initialize(_executor);
        }