Unify advanceTimersByTime and flushPromises

Ports testing-library/dom-testing-library#1229

Author: Sebastian Silbermann

src/__tests__/waitFor.test.js

@@ -176,15 +176,9 @@ test('does not work after it resolves', async () => {
 
 /** @type {import('../').FakeClock} */
 const jestFakeClock = {
-  advanceTimersByTime: timeoutMS => {
+  advanceTimersByTime: async timeoutMS => {
     jest.advanceTimersByTime(timeoutMS)
   },
-  flushPromises: () => {
-    return new Promise(r => {
-      setTimeout(r, 0)
-      jest.advanceTimersByTime(0)
-    })
-  },
 }
 describe.each([
   ['real timers', {useTimers: () => jest.useRealTimers(), clock: undefined}],

src/__tests__/waitForDOM.test.js

@@ -65,6 +65,11 @@ function waitFor(
     return error
   }
 
+  /**
+   * @template T
+   * @param {() => T} cb 
+   * @returns T
+   */
   function advanceTimersWrapper(cb) {
     // /dom config. /react uses act() here
     return cb()
@@ -78,16 +83,8 @@ function waitFor(
   /** @type {import('../').FakeClock} */
   const jestFakeClock = {
     advanceTimersByTime: timeoutMS => {
-      advanceTimersWrapper(() => {
-        jest.advanceTimersByTime(timeoutMS)
-      })
-    },
-    flushPromises: () => {
       return advanceTimersWrapper(async () => {
-        await new Promise(r => {
-          setTimeout(r, 0)
-          jest.advanceTimersByTime(0)
-        })
+        jest.advanceTimersByTime(timeoutMS)
       })
     },
   }

src/__tests__/waitForNode.js renamed to src/__tests__/waitForNode.test.js

@@ -37,15 +37,9 @@ function jestFakeTimersAreEnabled() {
 function waitFor(callback, options) {
   /** @type {import('../').FakeClock} */
   const jestFakeClock = {
-    advanceTimersByTime: timeoutMS => {
+    advanceTimersByTime: async timeoutMS => {
       jest.advanceTimersByTime(timeoutMS)
     },
-    flushPromises: () => {
-      return new Promise(r => {
-        setTimeout(r, 0)
-        jest.advanceTimersByTime(0)
-      })
-    },
   }
   const clock = jestFakeTimersAreEnabled() ? jestFakeClock : undefined
 
@@ -210,15 +204,15 @@ describe('using fake modern timers', () => {
     // An actual test would not have any frames pointing to this test.
     expect(waitForError.stack).toMatchInlineSnapshot(`
       Error: Timed out in waitFor.
-          at handleTimeout (<PROJECT_ROOT>/src/waitFor.ts:146:17)
+          at handleTimeout (<PROJECT_ROOT>/src/waitFor.ts:139:17)
           at callTimer (<PROJECT_ROOT>/node_modules/@sinonjs/fake-timers/src/fake-timers-src.js:729:24)
           at doTickInner (<PROJECT_ROOT>/node_modules/@sinonjs/fake-timers/src/fake-timers-src.js:1289:29)
           at doTick (<PROJECT_ROOT>/node_modules/@sinonjs/fake-timers/src/fake-timers-src.js:1370:20)
           at Object.tick (<PROJECT_ROOT>/node_modules/@sinonjs/fake-timers/src/fake-timers-src.js:1378:20)
           at FakeTimers.advanceTimersByTime (<PROJECT_ROOT>/node_modules/@jest/fake-timers/build/modernFakeTimers.js:101:19)
           at Object.advanceTimersByTime (<PROJECT_ROOT>/node_modules/jest-runtime/build/index.js:2228:26)
-          at Object.advanceTimersByTime (<PROJECT_ROOT>/src/__tests__/waitForNode.js:41:12)
-          at <PROJECT_ROOT>/src/waitFor.ts:80:15
+          at Object.advanceTimersByTime (<PROJECT_ROOT>/src/__tests__/waitForNode.test.js:41:12)
+          at <PROJECT_ROOT>/src/waitFor.ts:85:21
           at new Promise (<anonymous>)
     `)
   })

src/waitFor.ts

@@ -7,7 +7,7 @@ function copyStackTrace(target: Error, source: Error) {
 }
 
 export interface FakeClock {
-  advanceTimersByTime: (timeoutMS: number) => void
+  advanceTimersByTime: (timeoutMS: number) => Promise<void>
   flushPromises: () => Promise<void>
 }
 
@@ -77,19 +77,12 @@ function waitForImpl<T>(
       // waiting or when we've timed out.
       // eslint-disable-next-line no-unmodified-loop-condition, @typescript-eslint/no-unnecessary-condition
       while (!finished && !signal?.aborted) {
-        clock.advanceTimersByTime(interval)
-
-        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition -- No it isn't
-        if (finished) {
-          break
-        }
-
         // In this rare case, we *need* to wait for in-flight promises
         // to resolve before continuing. We don't need to take advantage
         // of parallelization so we're fine.
         // https://stackoverflow.com/a/59243586/971592
         // eslint-disable-next-line no-await-in-loop
-        await clock.flushPromises()
+        await clock.advanceTimersByTime(interval)
       }
     }