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WWDC20 · 14 min · Developer Tools

Eliminate animation hitches with XCTest

Animations can dramatically enhance the user experience of your app, provide a sense of direct manipulation, and help people to better understand the results of their actions. Animation hitches can break that experience. Discover how to use XCTest to detect interruptions to smooth scrolling and animations, and learn how to catch regressions before they affect the people relying on your app.

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Code shown on screen · 4 snippets

Create an animation os_signpost interval swift · at 6:35 ↗ 
os_signpost(.animationBegin, log: logHandle, name: "performAnimationInterval")
os_signpost(.end, log: logHandle, name: "performAnimationInterval")
Use a UIKit instrumented animation os_signpost interval swift · at 6:55 ↗ 
extension XCTOSSignpostMetric {
     open class var navigationTransitionMetric: XCTMetric { get }
     open class var customNavigationTransitionMetric: XCTMetric { get }
     open class var scrollDecelerationMetric: XCTMetric { get }
     open class var scrollDraggingMetric: XCTMetric { get }
}
Measure scrolling animation performance using a Performance XCTest swift · at 7:12 ↗ 
// Measure scrolling animation performance using a Performance XCTest
func testScrollingAnimationPerformance() throws {
    app.launch()
    app.staticTexts["Meal Planner"].tap()
    let foodCollection = app.collectionViews.firstMatch
    
    measure(metrics: [XCTOSSignpostMetric.scrollDecelerationMetric]) {
        foodCollection.swipeUp(velocity: .fast)
    }
}
Reset the application state between runs swift · at 8:02 ↗ 
func testScrollingAnimationPerformance() throws { 
    app.launch()
    app.staticTexts["Meal Planner"].tap()
    let foodCollection = app.collectionViews.firstMatch

    let measureOptions = XCTMeasureOptions()
    measureOptions.invocationOptions = [.manuallyStop]
        
    measure(metrics: [XCTOSSignpostMetric.scrollDecelerationMetric],
            options: measureOptions) {
        foodCollection.swipeUp(velocity: .fast)
        stopMeasuring()
        foodCollection.swipeDown(velocity: .fast)
    }
}