feat: add expect.poll utility

docs/.vitepress/components.d.ts

@@ -1,10 +1,10 @@
 /* eslint-disable */
-/* prettier-ignore */
 // @ts-nocheck
 // Generated by unplugin-vue-components
 // Read more: https://github.com/vuejs/core/pull/3399
 export {}
 
+/* prettier-ignore */
 declare module 'vue' {
   export interface GlobalComponents {
     Contributors: typeof import('./components/Contributors.vue')['default']
@@ -13,8 +13,6 @@ declare module 'vue' {
     HomePage: typeof import('./components/HomePage.vue')['default']
     ListItem: typeof import('./components/ListItem.vue')['default']
     NonProjectOption: typeof import('./components/NonProjectOption.vue')['default']
-    RouterLink: typeof import('vue-router')['RouterLink']
-    RouterView: typeof import('vue-router')['RouterView']
     Version: typeof import('./components/Version.vue')['default']
   }
 }

docs/api/expect.md

@@ -59,6 +59,47 @@ test('expect.soft test', () => {
 `expect.soft` can only be used inside the [`test`](/api/#test) function.
 :::
 
+## poll
+
+- **Type:** `ExpectStatic & (actual: () => any, options: { interval, timeout, message }) => Assertions`
+
+`expect.poll` reruns the _assertion_ until it is succeeded. You can configure how many times Vitest should rerun the `expect.poll` callback by setting `interval` and `timeout` options.
+
+If an error is thrown inside the `expect.poll` callback, Vitest will retry again until the timeout runs out.
+
+```ts twoslash
+function asyncInjectElement() {
+  // example function
+}
+
+// ---cut---
+import { expect, test } from 'vitest'
+
+test('element exists', async () => {
+  asyncInjectElement()
+
+  await expect.poll(() => document.querySelector('.element')).toBeTruthy()
+})
+```
+
+::: warning
+`expect.poll` makes every assertion asynchronous, so do not forget to await it otherwise you might get unhandled promise rejections.
+
+`expect.poll` doesn't work with several matchers:
+
+- Snapshot matchers are not supported because they will always succeed. If your condition is flaky, consider using [`vi.waitFor`](/api/vi#vi-waitfor) instead to resolve it first:
+
+```ts
+import { expect, vi } from 'vitest'
+
+const flakyValue = await vi.waitFor(() => getFlakyValue())
+expect(flakyValue).toMatchSnapshot()
+```
+
+- `.resolves` and `.rejects` are not supported. `expect.poll` already awaits the condition if it's asynchronous.
+- `toThrow` and its aliases are not supported because the `expect.poll` condition is always resolved before the matcher gets the value
+:::
+
 ## not
 
 Using `not` will negate the assertion. For example, this code asserts that an `input` value is not equal to `2`. If it's equal, the assertion will throw an error, and the test will fail.

packages/expect/src/jest-expect.ts

@@ -722,13 +722,23 @@ export const JestChaiExpect: ChaiPlugin = (chai, utils) => {
     return this.be.satisfy(matcher, message)
   })
 
+  // @ts-expect-error @internal
+  def('withContext', function (this: any, context: Record<string, any>) {
+    for (const key in context)
+      utils.flag(this, key, context[key])
+    return this
+  })
+
   utils.addProperty(chai.Assertion.prototype, 'resolves', function __VITEST_RESOLVES__(this: any) {
     const error = new Error('resolves')
     utils.flag(this, 'promise', 'resolves')
     utils.flag(this, 'error', error)
     const test: Test = utils.flag(this, 'vitest-test')
     const obj = utils.flag(this, 'object')
 
+    if (utils.flag(this, 'poll'))
+      throw new SyntaxError(`expect.poll() is not supported in combination with .resolves`)
+
     if (typeof obj?.then !== 'function')
       throw new TypeError(`You must provide a Promise to expect() when using .resolves, not '${typeof obj}'.`)
 
@@ -772,6 +782,9 @@ export const JestChaiExpect: ChaiPlugin = (chai, utils) => {
     const obj = utils.flag(this, 'object')
     const wrapper = typeof obj === 'function' ? obj() : obj // for jest compat
 
+    if (utils.flag(this, 'poll'))
+      throw new SyntaxError(`expect.poll() is not supported in combination with .rejects`)
+
     if (typeof wrapper?.then !== 'function')
       throw new TypeError(`You must provide a Promise to expect() when using .rejects, not '${typeof wrapper}'.`)
 

packages/expect/src/jest-extend.ts

@@ -40,6 +40,8 @@ function getMatcherState(assertion: Chai.AssertionStatic & Chai.Assertion, expec
     equals,
     // needed for built-in jest-snapshots, but we don't use it
     suppressedErrors: [],
+    soft: util.flag(assertion, 'soft') as boolean | undefined,
+    poll: util.flag(assertion, 'poll') as boolean | undefined,
   }
 
   return {

packages/expect/src/types.ts

@@ -70,6 +70,7 @@ export interface MatcherState {
     subsetEquality: Tester
   }
   soft?: boolean
+  poll?: boolean
 }
 
 export interface SyncExpectationResult {
@@ -91,12 +92,7 @@ export type MatchersObject<T extends MatcherState = MatcherState> = Record<strin
 
 export interface ExpectStatic extends Chai.ExpectStatic, AsymmetricMatchersContaining {
   <T>(actual: T, message?: string): Assertion<T>
-  unreachable: (message?: string) => never
-  soft: <T>(actual: T, message?: string) => Assertion<T>
   extend: (expects: MatchersObject) => void
-  addEqualityTesters: (testers: Array<Tester>) => void
-  assertions: (expected: number) => void
-  hasAssertions: () => void
   anything: () => any
   any: (constructor: unknown) => any
   getState: () => MatcherState
@@ -175,13 +171,15 @@ type Promisify<O> = {
     : O[K]
 }
 
+export type PromisifyAssertion<T> = Promisify<Assertion<T>>
+
 export interface Assertion<T = any> extends VitestAssertion<Chai.Assertion, T>, JestAssertion<T> {
   toBeTypeOf: (expected: 'bigint' | 'boolean' | 'function' | 'number' | 'object' | 'string' | 'symbol' | 'undefined') => void
   toHaveBeenCalledOnce: () => void
   toSatisfy: <E>(matcher: (value: E) => boolean, message?: string) => void
 
-  resolves: Promisify<Assertion<T>>
-  rejects: Promisify<Assertion<T>>
+  resolves: PromisifyAssertion<T>
+  rejects: PromisifyAssertion<T>
 }
 
 declare global {

packages/expect/src/utils.ts

@@ -1,8 +1,6 @@
 import { processError } from '@vitest/utils/error'
 import type { Test } from '@vitest/runner/types'
-import { GLOBAL_EXPECT } from './constants'
-import { getState } from './state'
-import type { Assertion, MatcherState } from './types'
+import type { Assertion } from './types'
 
 export function recordAsyncExpect(test: any, promise: Promise<any> | PromiseLike<any>) {
   // record promise for test, that resolves before test ends
@@ -25,16 +23,11 @@ export function recordAsyncExpect(test: any, promise: Promise<any> | PromiseLike
 
 export function wrapSoft(utils: Chai.ChaiUtils, fn: (this: Chai.AssertionStatic & Assertion, ...args: any[]) => void) {
   return function (this: Chai.AssertionStatic & Assertion, ...args: any[]) {
-    const test: Test = utils.flag(this, 'vitest-test')
-
-    // @ts-expect-error local is untyped
-    const state: MatcherState = test?.context._local
-      ? test.context.expect.getState()
-      : getState((globalThis as any)[GLOBAL_EXPECT])
-
-    if (!state.soft)
+    if (!utils.flag(this, 'soft'))
       return fn.apply(this, args)
 
+    const test: Test = utils.flag(this, 'vitest-test')
+
     if (!test)
       throw new Error('expect.soft() can only be used inside a test')
 

packages/vitest/src/integrations/chai/index.ts

@@ -9,11 +9,12 @@ import type { Assertion, ExpectStatic } from '@vitest/expect'
 import type { MatcherState } from '../../types/chai'
 import { getTestName } from '../../utils/tasks'
 import { getCurrentEnvironment, getWorkerState } from '../../utils/global'
+import { createExpectPoll } from './poll'
 
 export function createExpect(test?: TaskPopulated) {
   const expect = ((value: any, message?: string): Assertion => {
     const { assertionCalls } = getState(expect)
-    setState({ assertionCalls: assertionCalls + 1, soft: false }, expect)
+    setState({ assertionCalls: assertionCalls + 1 }, expect)
     const assert = chai.expect(value, message) as unknown as Assertion
     const _test = test || getCurrentTest()
     if (_test)
@@ -51,13 +52,12 @@ export function createExpect(test?: TaskPopulated) {
     addCustomEqualityTesters(customTesters)
 
   expect.soft = (...args) => {
-    const assert = expect(...args)
-    expect.setState({
-      soft: true,
-    })
-    return assert
+    // @ts-expect-error private soft access
+    return expect(...args).withContext({ soft: true }) as Assertion
   }
 
+  expect.poll = createExpectPoll(expect)
+
   expect.unreachable = (message?: string) => {
     chai.assert.fail(`expected${message ? ` "${message}" ` : ' '}not to be reached`)
   }

packages/vitest/src/integrations/chai/poll.ts

@@ -0,0 +1,75 @@
+import * as chai from 'chai'
+import type { ExpectStatic } from '@vitest/expect'
+import { getSafeTimers } from '@vitest/utils'
+
+// these matchers are not supported because they don't make sense with poll
+const unsupported = [
+  // .poll is meant to retry matchers until they succeed, and
+  // snapshots will always succeed as long as the poll method doesn't thow an error
+  // in this case using the `vi.waitFor` method is more appropriate
+  'matchSnapshot',
+  'toMatchSnapshot',
+  'toMatchInlineSnapshot',
+  'toThrowErrorMatchingSnapshot',
+  'toThrowErrorMatchingInlineSnapshot',
+  // toThrow will never succeed because we call the poll callback until it doesn't throw
+  'throws',
+  'Throw',
+  'throw',
+  'toThrow',
+  'toThrowError',
+  // these are not supported because you can call them without `.poll`,
+  // we throw an error inside the rejects/resolves methods to prevent this
+  // rejects,
+  // resolves
+]
+
+export function createExpectPoll(expect: ExpectStatic): ExpectStatic['poll'] {
+  return function poll(fn, options = {}) {
+    const { interval = 50, timeout = 1000, message } = options
+    const STACK_TRACE_ERROR = new Error('STACK_TRACE_ERROR')
+    // @ts-expect-error private poll access
+    const assertion = expect(null, message).withContext({ poll: true }) as Assertion
+    const proxy: any = new Proxy(assertion, {
+      get(target, key, receiver) {
+        const result = Reflect.get(target, key, receiver)
+
+        if (typeof result !== 'function')
+          return result instanceof chai.Assertion ? proxy : result
+
+        if (typeof key === 'string' && unsupported.includes(key))
+          throw new SyntaxError(`expect.poll() is not supported in combination with .${key}(). Use vi.waitFor() if your assertion condition is unstable.`)
+
+        return function (this: any, ...args: any[]) {
+          return new Promise((resolve, reject) => {
+            let intervalId: any
+            let lastError: any
+            const { setTimeout } = getSafeTimers()
+            setTimeout(() => {
+              clearTimeout(intervalId)
+              reject(copyStackTrace(new Error(`Matcher did not succeed in ${timeout}ms`, { cause: lastError }), STACK_TRACE_ERROR))
+            }, timeout)
+            const check = async () => {
+              try {
+                chai.util.flag(this, 'object', await fn())
+                resolve(await result.call(this, ...args))
+              }
+              catch (err) {
+                lastError = err
+                intervalId = setTimeout(check, interval)
+              }
+            }
+            check()
+          })
+        }
+      },
+    })
+    return proxy
+  }
+}
+
+function copyStackTrace(target: Error, source: Error) {
+  if (source.stack !== undefined)
+    target.stack = source.stack.replace(source.message, target.message)
+  return target
+}

packages/vitest/src/node/error.ts

@@ -160,6 +160,8 @@ const skipErrorProperties = new Set([
   'stackStr',
   'type',
   'showDiff',
+  'ok',
+  'operator',
   'diff',
   'codeFrame',
   'actual',

packages/vitest/src/types/global.ts

@@ -1,6 +1,6 @@
 import type { Plugin as PrettyFormatPlugin } from 'pretty-format'
 import type { SnapshotState } from '@vitest/snapshot'
-import type { ExpectStatic } from '@vitest/expect'
+import type { ExpectStatic, PromisifyAssertion, Tester } from '@vitest/expect'
 import type { UserConsoleLog } from './general'
 import type { VitestEnvironment } from './config'
 import type { BenchmarkResult } from './benchmark'
@@ -33,7 +33,19 @@ declare module '@vitest/expect' {
     snapshotState: SnapshotState
   }
 
+  interface ExpectPollOptions {
+    interval?: number
+    timeout?: number
+    message?: string
+  }
+
   interface ExpectStatic {
+    unreachable: (message?: string) => never
+    soft: <T>(actual: T, message?: string) => Assertion<T>
+    poll: <T>(actual: () => T, options?: ExpectPollOptions) => PromisifyAssertion<Awaited<T>>
+    addEqualityTesters: (testers: Array<Tester>) => void
+    assertions: (expected: number) => void
+    hasAssertions: () => void
     addSnapshotSerializer: (plugin: PrettyFormatPlugin) => void
   }
 

test/core/test/expect-poll.test.ts

@@ -0,0 +1,63 @@
+import { expect, test, vi } from 'vitest'
+
+// TODO: add custom matcher test
+
+test('simple usage', async () => {
+  await expect.poll(() => false).toBe(false)
+  await expect.poll(() => false).not.toBe(true)
+  // .resolves allowed after .poll
+  await expect(Promise.resolve(1)).resolves.toBe(1)
+
+  await expect(async () => {
+    await expect.poll(() => Promise.resolve(1)).resolves.toBe(1)
+  }).rejects.toThrowError('expect.poll() is not supported in combination with .resolves')
+  await expect(async () => {
+    await expect.poll(() => Promise.reject(new Error('empty'))).rejects.toThrowError('empty')
+  }).rejects.toThrowError('expect.poll() is not supported in combination with .rejects')
+
+  const unsupported = [
+    'matchSnapshot',
+    'toMatchSnapshot',
+    'toMatchInlineSnapshot',
+    'throws',
+    'Throw',
+    'throw',
+    'toThrow',
+    'toThrowError',
+    'toThrowErrorMatchingSnapshot',
+    'toThrowErrorMatchingInlineSnapshot',
+  ] as const
+
+  for (const key of unsupported) {
+    await expect(async () => {
+      await expect.poll(() => Promise.resolve(1))[key as 'matchSnapshot']()
+    }).rejects.toThrowError(`expect.poll() is not supported in combination with .${key}(). Use vi.waitFor() if your assertion condition is unstable.`)
+  }
+})
+
+test('timeout', async () => {
+  await expect(async () => {
+    await expect.poll(() => false, { timeout: 100 }).toBe(true)
+  }).rejects.toThrowError('Matcher did not succeed in 100ms')
+})
+
+test('interval', async () => {
+  const fn = vi.fn(() => true)
+  await expect(async () => {
+    // using big values because CI can be slow
+    await expect.poll(fn, { interval: 100, timeout: 500 }).toBe(false)
+  }).rejects.toThrowError()
+  // CI can be unstable, but there should be always at least 5 calls
+  expect(fn.mock.calls.length >= 5).toBe(true)
+})
+
+test('fake timers don\'t break it', async () => {
+  const now = Date.now()
+  vi.useFakeTimers()
+  await expect(async () => {
+    await expect.poll(() => false, { timeout: 100 }).toBe(true)
+  }).rejects.toThrowError('Matcher did not succeed in 100ms')
+  vi.useRealTimers()
+  const diff = Date.now() - now
+  expect(diff >= 100).toBe(true)
+})