feat(vitest): add vi.advanceTimersToNextFrame (#6347)

Co-authored-by: Vladimir <sleuths.slews0s@icloud.com>

Author: bnjm

docs/api/vi.md

@@ -603,6 +603,24 @@ await vi.advanceTimersToNextTimerAsync() // log: 2
 await vi.advanceTimersToNextTimerAsync() // log: 3
 ```
 
+### vi.advanceTimersToNextFrame <Version>2.1.0</Version> {#vi-advancetimerstonextframe}
+
+- **Type:** `() => Vitest`
+
+Similar to [`vi.advanceTimersByTime`](https://vitest.dev/api/vi#vi-advancetimersbytime), but will advance timers by the milliseconds needed to execute callbacks currently scheduled with `requestAnimationFrame`.
+
+```ts
+let frameRendered = false
+
+requestAnimationFrame(() => {
+  frameRendered = true
+})
+
+vi.advanceTimersToNextFrame()
+
+expect(frameRendered).toBe(true)
+```
+
 ### vi.getTimerCount
 
 - **Type:** `() => number`

packages/vitest/src/integrations/mock/timers.ts

@@ -113,6 +113,12 @@ export class FakeTimers {
     }
   }
 
+  advanceTimersToNextFrame(): void {
+    if (this._checkFakeTimers()) {
+      this._clock.runToFrame()
+    }
+  }
+
   runAllTicks(): void {
     if (this._checkFakeTimers()) {
       // @ts-expect-error method not exposed

packages/vitest/src/integrations/vi.ts

@@ -73,6 +73,10 @@ export interface VitestUtils {
    * Will call next available timer and wait until it's resolved if it was set asynchronously. Useful to make assertions between each timer call.
    */
   advanceTimersToNextTimerAsync: () => Promise<VitestUtils>
+  /**
+   * Similar to [`vi.advanceTimersByTime`](https://vitest.dev/api/vi#vi-advancetimersbytime), but will advance timers by the milliseconds needed to execute callbacks currently scheduled with `requestAnimationFrame`.
+   */
+  advanceTimersToNextFrame: () => VitestUtils
   /**
    * Get the number of waiting timers.
    */
@@ -511,6 +515,11 @@ function createVitest(): VitestUtils {
       return utils
     },
 
+    advanceTimersToNextFrame() {
+      timers().advanceTimersToNextFrame()
+      return utils
+    },
+
     getTimerCount() {
       return timers().getTimerCount()
     },

test/core/test/fixtures/timers.suite.ts

@@ -811,6 +811,202 @@ describe('FakeTimers', () => {
     })
   })
 
+  describe('advanceTimersToNextFrame', () => {
+    it('runs scheduled animation frame callbacks in order', () => {
+      const global = {
+        Date,
+        clearTimeout,
+        process,
+        requestAnimationFrame: () => -1,
+        setTimeout,
+      } as unknown as typeof globalThis
+
+      const timers = new FakeTimers({ global })
+      timers.useFakeTimers()
+
+      const runOrder: Array<string> = []
+      const mock1 = vi.fn(() => runOrder.push('mock1'))
+      const mock2 = vi.fn(() => runOrder.push('mock2'))
+      const mock3 = vi.fn(() => runOrder.push('mock3'))
+
+      global.requestAnimationFrame(mock1)
+      global.requestAnimationFrame(mock2)
+      global.requestAnimationFrame(mock3)
+
+      timers.advanceTimersToNextFrame()
+
+      expect(runOrder).toEqual(['mock1', 'mock2', 'mock3'])
+    })
+
+    it('should only run currently scheduled animation frame callbacks', () => {
+      const global = {
+        Date,
+        clearTimeout,
+        process,
+        requestAnimationFrame: () => -1,
+        setTimeout,
+      } as unknown as typeof globalThis
+
+      const timers = new FakeTimers({ global })
+      timers.useFakeTimers()
+
+      const runOrder: Array<string> = []
+      function run() {
+        runOrder.push('first-frame')
+
+        // scheduling another animation frame in the first frame
+        global.requestAnimationFrame(() => runOrder.push('second-frame'))
+      }
+
+      global.requestAnimationFrame(run)
+
+      // only the first frame should be executed
+      timers.advanceTimersToNextFrame()
+
+      expect(runOrder).toEqual(['first-frame'])
+
+      timers.advanceTimersToNextFrame()
+
+      expect(runOrder).toEqual(['first-frame', 'second-frame'])
+    })
+
+    it('should allow cancelling of scheduled animation frame callbacks', () => {
+      const global = {
+        Date,
+        cancelAnimationFrame: () => {},
+        clearTimeout,
+        process,
+        requestAnimationFrame: () => -1,
+        setTimeout,
+      } as unknown as typeof globalThis
+
+      const timers = new FakeTimers({ global })
+      const callback = vi.fn()
+      timers.useFakeTimers()
+
+      const timerId = global.requestAnimationFrame(callback)
+      global.cancelAnimationFrame(timerId)
+
+      timers.advanceTimersToNextFrame()
+
+      expect(callback).not.toHaveBeenCalled()
+    })
+
+    it('should only advance as much time is needed to get to the next frame', () => {
+      const global = {
+        Date,
+        cancelAnimationFrame: () => {},
+        clearTimeout,
+        process,
+        requestAnimationFrame: () => -1,
+        setTimeout,
+      } as unknown as typeof globalThis
+
+      const timers = new FakeTimers({ global })
+      timers.useFakeTimers()
+
+      const runOrder: Array<string> = []
+      const start = global.Date.now()
+
+      const callback = () => runOrder.push('frame')
+      global.requestAnimationFrame(callback)
+
+      // Advancing timers less than a frame (which is 16ms)
+      timers.advanceTimersByTime(6)
+      expect(global.Date.now()).toEqual(start + 6)
+
+      // frame not yet executed
+      expect(runOrder).toEqual([])
+
+      // move timers forward to execute frame
+      timers.advanceTimersToNextFrame()
+
+      // frame has executed as time has moved forward 10ms to get to the 16ms frame time
+      expect(runOrder).toEqual(['frame'])
+      expect(global.Date.now()).toEqual(start + 16)
+    })
+
+    it('should execute any timers on the way to the animation frame', () => {
+      const global = {
+        Date,
+        cancelAnimationFrame: () => {},
+        clearTimeout,
+        process,
+        requestAnimationFrame: () => -1,
+        setTimeout,
+      } as unknown as typeof globalThis
+
+      const timers = new FakeTimers({ global })
+      timers.useFakeTimers()
+
+      const runOrder: Array<string> = []
+
+      global.requestAnimationFrame(() => runOrder.push('frame'))
+
+      // scheduling a timeout that will be executed on the way to the frame
+      global.setTimeout(() => runOrder.push('timeout'), 10)
+
+      // move timers forward to execute frame
+      timers.advanceTimersToNextFrame()
+
+      expect(runOrder).toEqual(['timeout', 'frame'])
+    })
+
+    it('should not execute any timers scheduled inside of an animation frame callback', () => {
+      const global = {
+        Date,
+        cancelAnimationFrame: () => {},
+        clearTimeout,
+        process,
+        requestAnimationFrame: () => -1,
+        setTimeout,
+      } as unknown as typeof globalThis
+
+      const timers = new FakeTimers({ global })
+      timers.useFakeTimers()
+
+      const runOrder: Array<string> = []
+
+      global.requestAnimationFrame(() => {
+        runOrder.push('frame')
+        // scheduling a timer inside of a frame
+        global.setTimeout(() => runOrder.push('timeout'), 1)
+      })
+
+      timers.advanceTimersToNextFrame()
+
+      // timeout not yet executed
+      expect(runOrder).toEqual(['frame'])
+
+      // validating that the timer will still be executed
+      timers.advanceTimersByTime(1)
+      expect(runOrder).toEqual(['frame', 'timeout'])
+    })
+
+    it('should call animation frame callbacks with the latest system time', () => {
+      const global = {
+        Date,
+        clearTimeout,
+        performance,
+        process,
+        requestAnimationFrame: () => -1,
+        setTimeout,
+      } as unknown as typeof globalThis
+
+      const timers = new FakeTimers({ global })
+      timers.useFakeTimers()
+
+      const callback = vi.fn()
+
+      global.requestAnimationFrame(callback)
+
+      timers.advanceTimersToNextFrame()
+
+      // `requestAnimationFrame` callbacks are called with a `DOMHighResTimeStamp`
+      expect(callback).toHaveBeenCalledWith(global.performance.now())
+    })
+  })
+
   describe('reset', () => {
     it('resets all pending setTimeouts', () => {
       const global = { Date: FakeDate, clearTimeout, process, setTimeout }