pointerEventSource property Null safety
The source of the current pointer event.
This means that pointer events triggered by the WidgetController (e.g. via WidgetController.tap) will result in actual interactions with the UI, but other pointer events such as those from physical taps will be dropped. See also shouldPropagateDevicePointerEvents if this is undesired.
TestBindingEventSource get pointerEventSource => _pointerEventSource;