test(query-core/subscribable): add unit tests for the Subscribable base class

[solssak]

🎯 Changes

Add a dedicated unit test file for the Subscribable base class in query-core.

Subscribable is the base class that QueryCache, MutationCache, QueryObserver, MutationObserver, QueriesObserver, FocusManager, and OnlineManager all extend, but it had no test file of its own — its behavior was only exercised indirectly through those subclasses. This PR tests the class directly so the core subscribe/unsubscribe contract is pinned down in one place.

The new subscribable.test.tsx uses a minimal test subclass that spies on the protected onSubscribe/onUnsubscribe hooks, and covers:

• onSubscribe fires once per subscribe() call
• onUnsubscribe fires when the returned unsubscribe function is called
• hasListeners() transitions correctly across subscribe/unsubscribe, including when multiple listeners are registered and only some unsubscribe
• the same listener reference is de-duplicated (the underlying Set semantics)
• the subscribe method stays bound to the instance when destructured (the this.subscribe = this.subscribe.bind(this) in the constructor)

No source code is changed — this only adds test coverage.

✅ Checklist

• I have followed the steps in the Contributing guide.
• I have tested this code locally with pnpm run test:pr.
• I fully understand the code in this pull request.

🚀 Release Impact

• This change affects published code, and I have generated a changeset.
• This change is docs/CI/dev-only (no release).

Summary by CodeRabbit

• Tests
  • Added comprehensive coverage for subscription behavior, including listener lifecycle hooks, listener state tracking, duplicate listener handling, and stable subscription references.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Team

Run ID: 112665cb-aae7-4919-9239-e26d978cffbe

📥 Commits

Reviewing files that changed from the base of the PR and between 40cb38d and c29253d.

📒 Files selected for processing (1)

• packages/query-core/src/__tests__/subscribable.test.tsx

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.

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📝 Walkthrough

Walkthrough

Added a new Subscribable test suite. The tests cover lifecycle hooks, listener state, duplicate listener references, and destructured subscribe calls.

Changes

Subscribable listener lifecycle

Layer / File(s)	Summary
Listener lifecycle and state tests packages/query-core/src/__tests__/subscribable.test.tsx	Defines lifecycle hook spies and tests subscription, unsubscription, hasListeners(), listener deduplication, and stable destructured subscribe behavior.

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

Merge Risk: ⚪ Minimal · up to c2925

This change adds focused tests for existing subscription behavior without modifying production code or runtime behavior. No actionable merge-blocking risk remains beyond normal checks and review.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the addition of unit tests for the query-core Subscribable base class.
Description check	✅ Passed	The description explains the change, motivation, test coverage, checklist status, and release impact. It matches the required template and confirms that no source code changes are included.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1…
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.

Full details: Docstring Coverage

Explanation

No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1 files.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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