Not precise scroll in XCTest

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I'm working on UI automation tests using XCUITest for an iOS application (iPhone). My goal is to programmatically scroll a view by a very precise number of pixels (e.g., exactly 500 points down). I understand the scroll(byDeltaX:deltaY:) method is not supported on iPhone, so I'm using the coordinate-based drag method as an alternative.

Specifically, I am using XCUICoordinate.press(forDuration:thenDragTo:withVelocity:thenHoldForDuration:) to simulate a drag gesture. I calculate a start and end coordinate with a specific vertical offset in points, expecting the view to scroll by that exact amount.

However, I'm observing that the resulting scroll offset is not perfectly accurate. There's a consistent error of several pixels, making the scroll amount unpredictable for precise test assertions.

Is there a known limitation to the accuracy of coordinate-based dragging for simulating programmatic scrolling? Are there any alternative methods or best practices within XCUITest to achieve a more reliable and pixel-accurate scroll on iPhone, or is this level of precision simply not achievable with the current framework?

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DTS Engineer OP

Apple

23h

Hello IvanPushkov,

Thanks for your question. XCUICoordinate.press(forDuration:thenDragTo:withVelocity:thenHoldForDuration:) is indeed a recommendable way to simulate scrolling in iOS XCUITests. You could potentially improve accuracy by ensuring that the coordinate is based on the top level element, such as the root view.

Could you possible create a focused test project that replicates the issue of miscalculating offsets, so we can troubleshoot it? If so, please share a link to your test project.

If you're not familiar with preparing a test project, take a look at Creating a test project.

Thank you,

Richard Yeh  Developer Technical Support

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