Summary

Mouse testing for RangeSlider widget is not supported in the current widget testing framework. The current mouse testing for widgets is done using the click_and_drag function, but it has no support for widgets without 'press' events.

Proposed fix

The click_and_drag function should be generalized in order to support more widgets. One solution would be adding support for sending events through the canvas.

This potential solution is mentioned here by @ianhi:
#22711 (comment)