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test(reader): de-flake scrolled-mode backward-preload precondition (#4112) (#4354)

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The two #4112 scrolled-mode preload browser tests asserted that the
previous-previous section (F-1) was not loaded after navigating to a section,
checking it after `waitForFillComplete()`.

The eager backward buffer (minPages) is suppressed while `#display` is
stabilizing, but pulls F-1 (and beyond) in on the first scroll events once the
fill settles. So the post-fill assertion raced the buffer: it passed locally but
failed intermittently on CI (loaded set [1,2,3,4,5]).

Assert the precondition the instant `#display` stabilizes — where the buffer is
provably suppressed and only the immediate-previous section is loaded — before
the fill settles. The eager buffer loading F-1 later is exactly what the second
test wants once it navigates back. Test-only; production behaviour is unchanged.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Huang Xin
2026-05-29 16:22:58 +08:00
committed by GitHub
parent 6405ba31c8
commit a848c142c8
1 changed files with 16 additions and 4 deletions
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apps/readest-app/src/__tests__/document/paginator-scrolled.browser.test.ts
+16 -4
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@@ -197,11 +197,17 @@ describe('Paginator scrolled mode (browser)', () => {
return null;
};
// 1) Navigate to M so #display preloads F above it.
// 1) Navigate to M so #display preloads F above it. Assert the loaded set
// the instant #display stabilizes: #display only pulls in the immediate
// previous section (F), and the scroll-handler backward buffer stays
// suppressed while #stabilizing. Everything below — up to the goTo(F)
// that is meant to prepend F-1 — runs synchronously, so the eager
// backward buffer can't pull F-1 in early and steal the measurement.
// (Waiting for the fill to settle first is racy: once #stabilizing ends
// the minPages backward buffer may pull F-1 in — readest/readest#4112.)
const stabilized = waitForStabilized(paginator);
await paginator.goTo({ index: M, anchor: 0 });
await stabilized;
await waitForFillComplete(paginator);
// F is loaded as the top view; F-1 has not been pulled in yet.
const loadedIndices = () => paginator.getContents().map((c) => c.index);
@@ -251,12 +257,18 @@ describe('Paginator scrolled mode (browser)', () => {
expect(F).toBeGreaterThan(0);
const M = F + 1;
// Navigate to M (preloads F above it); F-1 is not loaded yet.
// Navigate to M (preloads F above it). Assert F-1 is not loaded the instant
// #display stabilizes — #display only pulls in the immediate previous
// section (F), and the scroll-handler backward buffer is suppressed while
// #stabilizing. Asserting after the fill settles is racy: once
// stabilization ends the eager minPages backward buffer may pull F-1 in
// (readest/readest#4112). It doing so later is fine — that is exactly what
// we want once we navigate back, below.
const stabilized = waitForStabilized(paginator);
await paginator.goTo({ index: M, anchor: 0 });
await stabilized;
await waitForFillComplete(paginator);
expect(paginator.getContents().map((c) => c.index)).not.toContain(F - 1);
await waitForFillComplete(paginator);
// Navigate one section back to F. The previous section (F-1) must be
// pre-loaded so the user can immediately scroll up into it.