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Fix a flaky reveal test #4

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Merged
crmapache merged 1 commit into from
Oct 16, 2026
Merged

Fix a flaky reveal test #4

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10 changes: 8 additions & 2 deletions tests/react.test.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@
import { act, render, cleanup } from '@testing-library/react'
import { StrictMode, createRef } from 'react'
import { renderToStaticMarkup } from 'react-dom/server'
import { afterEach, describe, expect, it } from 'vitest'
import { afterEach, describe, expect, it, onTestFinished, vi } from 'vitest'
import {
Reveal,
RevealProvider,
Expand Down Expand Up @@ -625,6 +625,10 @@ describe('settings that change at runtime', () => {

describe('RevealProvider resetKey', () => {
it('starts a new message on a fresh queue, even for a paragraph mounted with the new key', () => {
// Delays are measured from the clock at each render. Frozen, they compare slot positions
// rather than how much real time happened to pass between two renders.
const now = vi.spyOn(performance, 'now').mockReturnValue(1000)
onTestFinished(() => now.mockRestore())
const message = (key: number, id: string, text: string) => (
<RevealProvider resetKey={key}>
<Reveal key={id} initialText="">
Expand All @@ -645,7 +649,9 @@ describe('RevealProvider resetKey', () => {
const before = delays()
rerender(message(2, 'new', 'a new answer, and more'))
const after = delays().slice(before.length)
expect(parseFloat(after[0])).toBeGreaterThanOrEqual(parseFloat(before.at(-1)!))
// A slot handed out again would come at least one stagger (36 ms) earlier; the tolerance
// only absorbs floating-point rounding once the queue is held at maxWaveLagMs.
expect(parseFloat(after[0])).toBeGreaterThanOrEqual(parseFloat(before.at(-1)!) - 0.001)
})

it('takes its slots once under StrictMode, which mounts every paragraph twice', () => {
Expand Down
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