Hit-testing in Waldo

FAQs regarding the use of hit-testing in Waldo tests.

What is hit-testing?

When iOS processes a touch event (for example, a tap or swipe), it walks the view hierarchy to find the closest UI element that will accept the event. If the first UI element tested won’t accept the event, iOS checks the next closest UI element, and so on. This process is called hit-testing.

The UIView class provides two methods to accomplish this:

-[UIView hitTest:withEvent:]
 -[UIView pointInside:withEvent:]

The UIView.hitTest(_:with:) method traverses the view hierarchy by calling the UIView.point(inside:with:) method of each subview to determine which subview should receive a touch event.

If UIView.point(inside:with:) returns true (or YES), then the subview’s hierarchy is similarly traversed until the frontmost view containing the specified point is found. If a view does not contain the point, its branch of the view hierarchy is ignored.

The UIView.point(inside:with:) method simply returns a Boolean value indicating whether the view contains the specified point.

How does Waldo use hit-testing?

Whether you are recording or replaying a test flow, or interacting with Waldo Live, Waldo continually analyzes the current view hierarchy of your app. To resolve ambiguities in the view hierarchy, Waldo employs hit-testing. In the vast majority of cases, Waldo is able to correctly analyze the view hierarchy.


Be Aware:

In rare cases, this analysis fails because the app overrides a hit-testing method in a problematic way.

How does overriding a hit-testing method cause problems for Waldo?

In a nutshell, overriding a hit-testing method may cause a problem for Waldo if it initiates any action that changes the view hierarchy.

For example: we have seen numerous cases where an override dismisses an overlay view (or even the target view itself). We have also seen cases where an app uses a 3rd-party library that includes a problematic override of a hit-testing method.

When can overriding a hit-testing method be used successfully with Waldo?

In general, an override that simply resizes the hit area, or that excludes a region of the hit area, will not be problematic for Waldo.


Example of a successful override

A common example is overriding the hit-testing method for a small button in order to increase its hit area to be in compliance with the minimum size suggested by Apple’s Human Interface Guidelines.