public class TestCaseScratch : TestCase
{
    public TestCaseScratch()
    {
        Children = new Drawable[]
        {
            new PassThroughInputManager
            {
                RelativeSizeAxes = Axes.Both,
                UseParentInput = true,
                Child = new InputBox { RelativeSizeAxes = Axes.Both }
            },
            new HiddenInputHandler { RelativeSizeAxes = Axes.Both }
        };
    }

    private class InputBox : Box
    {
        protected override bool OnKeyDown(KeyDownEvent e)
        {
            Colour = Color4.Red;
            return true;
        }

        protected override bool OnKeyUp(KeyUpEvent e)
        {
            Colour = Color4.White;
            return true;
        }
    }

    private class HiddenInputHandler : Box
    {
        public HiddenInputHandler()
        {
            Alpha = 0;
            AlwaysPresent = true;
        }

        protected override bool Handle(UIEvent e) => true;
    }
}