Compose offers ComposeTestRule that allows you to write tests for animations
in a deterministic manner with full control over the test clock. This allows you
to verify intermediate animation values. In addition, a test can run quicker
than the actual duration of the animation.
ComposeTestRule exposes its test clock as mainClock. You can set the
autoAdvance property to false to control the clock in your test code. After
initiating the animation you want to test, the clock can be moved forward with
advanceTimeBy.
One thing to note here is that advanceTimeBy doesn't move the clock exactly by
the specified duration. Rather, it rounds it up to the nearest duration that is
a multiplier of the frame duration.
@get:Rule val rule = createComposeRule() @Test fun testAnimationWithClock() { // Pause animations rule.mainClock.autoAdvance = false var enabled by mutableStateOf(false) rule.setContent { val color by animateColorAsState( targetValue = if (enabled) Color.Red else Color.Green, animationSpec = tween(durationMillis = 250) ) Box(Modifier.size(64.dp).background(color)) } // Initiate the animation. enabled = true // Let the animation proceed. rule.mainClock.advanceTimeBy(50L) // Compare the result with the image showing the expected result. // `assertAgainGolden` needs to be implemented in your code. rule.onRoot().captureToImage().assertAgainstGolden() }
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