De-flake three unit tests (async ordering, sync timeout, off-main Core Data)

[jkmassel]

Three independent, test-only fixes for unit tests flagged flaky in Buildkite Test Engine. Each is a root-cause fix in a different test file; no production code changes.

Summary

• CommentDetailViewModelTests.actionsWaitForReplyCountAfterDetailRenders (46% reliability) — the test synchronized on the wrong async signal, then asserted on unrelated state.
• BlogJetpackTests.testSyncBlogsAndSignOut (84%) — a 1.0s expectation timeout, where the two sibling tests exercising the same sync pipeline wait 5.0s.
• ReaderTopicServiceTest.testReaderSiteTopicUpdated (94%) — the suite's only async test, un-@MainActor'd, drove mainContext Core Data off the main queue.

Root Cause & Fix

1. actionsWaitForReplyCountAfterDetailRenders — wait on the state the assertion checks

vm.onAppear() kicks off two independent, unordered MainActor tasks: a comment fetch and a reply-count fetch. The test waited until the reply-count call was recorded, then asserted on the comment-detail state (vm.content == .loaded(detail)). Those are set by different continuations with no happens-before edge, and waitUntil checks its predicate before the first Task.yield() — so it returned as soon as the reply-count invocation was recorded, often before the fetch continuation ran applyLoaded(detail). ~half the runs observed content still .loading.

Fix: wait on the state the assertion actually checks, keeping the existing conjunct that the later resolveNumberOfReplies relies on.

-        await waitUntil { !service.numberOfRepliesInvocations.isEmpty }
+        await waitUntil { vm.content == .loaded(detail) && !service.numberOfRepliesInvocations.isEmpty }

2. testSyncBlogsAndSignOut — match the sibling timeout

The sync always completes, but under CI CPU contention it occasionally crosses 1s (a low-priority .global(qos: .background) notify hop in the capabilities fan-out adds jitter). The two sibling tests that drive the same syncBlogs pipeline wait 5.0s and don't flake.

-        wait(for: [syncExpectation], timeout: 1.0)
+        wait(for: [syncExpectation], timeout: 5.0)

3. testReaderSiteTopicUpdated — pin to the main thread

This is the only async test in ReaderTopicSwiftTest and it is not @MainActor, so its body runs on a background cooperative thread. Its seeding helpers create/relate ReaderPost/ReaderSiteTopic objects and save() on the main-queue mainContext. Off-queue Core Data access nondeterministically corrupts the store bookkeeping, surfacing ~6% of runs as NSCocoaErrorDomain 133010 "Cannot save objects with references outside of their own stores". The other 8 tests are synchronous (main-thread) and never flake. The awaits still suspend and free the main thread for the OHHTTPStubs response and the main-queue completion, so there's no deadlock.

-    func testReaderSiteTopicUpdated() async throws {
+    @MainActor func testReaderSiteTopicUpdated() async throws {

Test plan

• Full suite green: xcodebuild -workspace WordPress.xcworkspace -scheme WordPress -testPlan WordPressUnitTests test (iOS 26.x sim, Xcode 26.6).
• Stress-run the 46% test ~100 iterations (-test-iterations 100 -run-tests-until-failure) — 0 failures.
• BlogJetpackTests and ReaderTopicSwiftTest green.
• Repeated CI runs green (this PR is validated by re-running CI, not a single pass).

[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress by scanning the QR code below to install the corresponding build.

	App Name	WordPress
	Configuration	Release-Alpha
	Build Number	34328
	Version	PR #25978
	Bundle ID	org.wordpress.alpha
	Commit	d912f9a
	Installation URL	2hh443v6g0dro

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[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack by scanning the QR code below to install the corresponding build.

	App Name	Jetpack
	Configuration	Release-Alpha
	Build Number	34328
	Version	PR #25978
	Bundle ID	com.jetpack.alpha
	Commit	d912f9a
	Installation URL	6ibrpfj44f6vg

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[dangermattic]

	1 Warning
⚠️	This PR is larger than 500 lines of changes. Please consider splitting it into smaller PRs for easier and faster reviews.

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[crazytonyli]

@jkmassel There some already-merged changes in this PR.

[jkmassel]

@jkmassel There some already-merged changes in this PR.

Yeah I goofed – there was a PR that kept failing because of the issue fixed by this PR and I wanted to stack them, but auto-merge was turned on, so when I changed the base it just merged instantly. Whoops!