Use case

I need to use WidgetTester.dragUntilVisible() (inherited from WidgetController.dragUntilVisible). The method takes a moveStep parameter of type Offset. I need to know what numerical dx and dy values to pass to the Offset constructor.

I discovered the information by trial-and-error. That took some time because of #88756, #88763 , #88759, and #88762. dragUntilVisible() uses a negative offset to scroll down, while scrollUntilVisible() uses a positive one.

Proposal

Update the docs to say:

moveStep is the movement of the virtual finger on the virtual screen. To swipe up (scroll down), use negative dy and dx=0. To swipe right, use positive dx and dy=0.