test(ui): poll for the copy failure state instead of a fixed tick budget

[kojiwakayama]

code-block.test.tsx › exposes failed copy feedback to assistive technology failed once in CI on #3474 — a branch that changes one line of CSP caching and no React code — and passed on re-run.

The race. settle spends a fixed budget of one microtask and one macrotask:

await Promise.resolve();
await new Promise((resolve) => setTimeout(resolve, 0));
flushSync(() => {});

That covers the success path, where the clipboard promise resolves and React re-renders. The failure path is longer: a rejected clipboard.writeText falls back to execCommand, and only once that returns false is the failed state set. On a loaded machine the assertion can run against the pre-failure render. It explains the shape of the flake exactly — only the two failure-path tests are exposed, and the success-path ones never flake.

The change. Both failure-path tests poll for the state they are actually about instead of guessing a tick count. The helper throws a named timeout, so a genuine regression still fails loudly rather than being waited out — I checked that by pointing the predicate at a sentinel that is never true and confirming it reports Timed out waiting for the copy control to report failure rather than passing.

What I cannot claim. I could not reproduce the flake locally: not in isolation (5/5 green), not with the whole ui/ directory in one process, not under --coverage, and not on a pristine origin/main worktree. So this removes a race that is visible in the code, not one I was able to observe. If it recurs, the timeout message will now say which condition was never reached, which is more than the previous failure gave us.

Separate from #3474 on purpose — an unrelated test-harness change does not belong in a one-line behavioural fix.

Summary by CodeRabbit

• Tests
  • Improved clipboard failure test reliability by waiting for asynchronous state updates.
  • Added timeout handling with clearer error feedback when expected updates do not occur.

[coderabbitai]

📝 Walkthrough

Walkthrough

The code-block tests add a polling helper for asynchronous state changes. Clipboard failure assertions now wait for the failed state and accessibility feedback instead of using a fixed delay.

Changes

Clipboard failure test synchronization

Layer / File(s)	Summary
Polling-based failure assertions src/react/components/ui/code-block.test.tsx	The tests add waitFor, which flushes updates and polls for expected state changes. Clipboard failure tests use it to wait for failed-copy state and accessibility feedback.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested reviewers: kwakayama

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main test change: polling for copy failure state instead of using a fixed tick budget.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/code-block-copy-test-race

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/react/components/ui/code-block.test.tsx`:
- Around line 76-82: Update waitFor to use a named timeout duration and a
deadline-based polling loop instead of the fixed 100-attempt limit. Continue
checking until the deadline is reached, and avoid sleeping after the final
failed predicate check before throwing the existing timeout error.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 1c97af67-e0bb-432a-82fc-77fc532b07e2

📥 Commits

Reviewing files that changed from the base of the PR and between 83ee058 and cf8f3c5.

📒 Files selected for processing (1)

• src/react/components/ui/code-block.test.tsx