MainTestClock

@JvmDefaultWithCompatibility
interface MainTestClock

The clock that drives frames, recompositions and launched effects in compose tests.

This clock is ultimately responsible for driving all recompositions, all subscribers to withFrameNanos (all compose animations) and all coroutines launched with LaunchedEffect (for example gesture detection). It is important to realize that if this clock does not tick, recomposition will not happen and animations are frozen.

Measure, layout and draw passes may be driven by this clock, depending on the platform. On Desktop, these are all driven by this clock, but on Android only measure and layout are performed synchronously. The draw pass on Android is driven by the Choreographer and will not happen as a result of forwarding this clock. Note that the Choreographer will also perform measure and layout passes, but these are mostly redundant because we will already have done the measure and layout pass as a result of forwarding this clock to recompose. That means that measure, layout and draw passes can still occur on Android even if this clock is paused.

Therefore, when setting autoAdvance to false and taking control over this clock, there are several things to realize:

• Recomposition can only happen when a frame is produced by this clock, with one exception: the initial composition when calling setContent happens immediately.
• Callers of withFrameNanos can only get a frame time when a frame is produced by this clock.
• If there is both a pending recomposition and an animation awaiting a frame time, ticking this clock will first send the new frame time to the animation, and then perform recomposition. Any state changes made by the animation will be seen by the recomposition.
• Because animations receive their frame time before recomposition, an animation will not get its start time in the first frame after kicking it off by toggling a state variable. For example, with a frame time of 16ms; when you call advanceTimeBy(32) after you toggled a state variable to kick off an animation, the animation's play time will still be at 0ms. The first frame is produced when the clock has advanced 16ms and will run a recomposition. During that recomposition the animation will be scheduled to start. When the clock has advanced another 16ms, the animation gets its first frame time and initialize the play time to t=0.
• Because animations request the next frame during the current frame, calling advanceTimeBy(160) while an animation is running will produce 10 frames of 16ms rather than 1 frame of 160ms (assuming a frame time of 16ms). Measure and layout happens after each frame, but draw will not happen in between these frames.
• After modifying a state variable, recomposition needs to happen to reflect the new state in the UI. Advancing the clock by one frame will commit the changes and run exactly one recomposition and measure and layout if triggered.
• If, after any call to advanceTimeBy, you want to assert anything related to rendering (e.g. SemanticsNodeInteraction.captureToImage), you will need a call to waitForIdle or runOnIdle to make sure that any triggered draw pass has been completed.
• If you change a state variable that is read during draw, calling advanceTimeBy will not produce the desired update to the UI. Use waitForIdle for this case.
• delayed LaunchedEffects are resumed on their scheduled time. That means that code like repeat(2) { delay(1000) } will complete with a single call to advanceTimeBy(2000).

Properties

val currentTime: Long

The current time of this clock in milliseconds.

var autoAdvance: Boolean

Whether the clock should be advanced by the testing framework while awaiting idleness in order to process any pending work that is driven by this clock. This ensures that when the app is idle, there are no more pending recompositions or ongoing animations.

If autoAdvance is false, the clock is not advanced while awaiting idleness. Moreover, having pending recompositions or animations is not taken as a sign of pending work (non-idleness) when awaiting idleness, as waiting for a longer time will not make them happen. Note that pending measure, layout or draw passes will still be awaited when awaiting idleness and having autoAdvance set to false, as those passes are not driven by this clock.

By default this is true.

Functions

fun advanceTimeByFrame()

Advances the main clock by the duration of one frame.

fun advanceTimeBy(milliseconds: Long, ignoreFrameDuration: Boolean = false)

Advances the clock by the given duration. The duration is rounded up to the nearest multiple of the frame duration by default to always produce the same number of frames regardless of the current time of the clock. Use ignoreFrameDuration to disable this behavior. The frame duration is platform dependent. For example, on a JVM (Android and Desktop) it is 16ms. Note that if ignoreFrameDuration is true, the last few milliseconds that are advanced might not be observed by anyone, since most processes are only triggered when a frame is produced.

When using this method to advance the time by several frames in one invocation, recomposition is done after each produced frame, but whether measure, layout and draw happen is platform dependent. On Android, measure and layout will be done, but not draw. On Desktop, measure, layout and draw will happen. Frames are only produced if there is a need for them, e.g. when an animation is running, or if state is changed. See MainTestClock for a more in depth explanation of the behavior of your test when controlling the clock.

It is recommended to set autoAdvance to false when using this method, but it is not strictly necessary. Manually advancing the time is just as fast as automatic advancement and vice versa.

Parameters

fun advanceTimeUntil(timeoutMillis: Long = 1_000, condition: () -> Boolean)

Advances the clock in increments of a single frame until the given condition is satisfied.

Note that the condition should only rely on things that are driven by this clock. Depending on the platform, measure, layout or draw passes might not happen in between advancements of the clock while waiting for the condition to become true. On Android and Desktop, measure and layout are happening, but draw only happens on Desktop. If your condition relies on the result of draw, use waitUntil instead.

See MainTestClock for a thorough explanation of what is and what isn't going to happen as a result of a call to advanceTimeBy.

Parameters