Automated testing strategy

[anomit]

Is your feature request related to a problem?

Yes. This repo’s snapshotter path has selection-aware process_task, deferred preloader-failure handling, batched MISSED_SNAPSHOT Telegram reporting, and related reconcile logic. Recent reviews noted that automated tests are still narrow: helpers such as format_missed_batch_summary are covered, but higher-risk paths—reconciliation on success/failure, send-not-before backoff, retry scheduling, preloader defer + reconcile—lack regression coverage. Without dev test dependencies and a CI step that runs them, mistakes can ship (for example, await on a synchronous defer_preloader_failure_notification). A small guard exists under snapshotter/tests/, but CI does not consistently install/run pytest from the Poetry graph.

Describe the solution you'd like

1. Dependencies — Add pytest (and minimal async tooling if adopted, e.g. pytest-asyncio) under [tool.poetry.group.dev.dependencies] in pyproject.toml, refresh poetry.lock, and document the test command in the README or CONTRIBUTING if present.
2. CI — Add a workflow job that installs with dev groups and runs e.g. poetry run pytest snapshotter/tests/ (adjust scope as needed).
3. Docker / production image — Use poetry install --no-root --without dev (or Poetry 2 --only main / equivalent) in the Dockerfile so the runtime image does not ship pytest (negligible incremental image size for production).
4. Tests (phased) — Add integration-style tests when bandwidth allows: stub httpx for Telegram, fake or temp-file SlotSelectionTracker, cover _try_reconcile_preloader_missed, _flush_missed_batch / retry paths, and the preloader-defer → reconcile flow.

Describe alternatives you've considered

• unittest only — No extra dev deps; weaker ergonomics for async and fixtures.
• pip install pytest in CI only — Works but diverges from the lockfile and local dev setup.
• Separate test image with dev deps — Heavier pipeline; optional follow-up.

Additional context

• Broader tests were intentionally deferred to a future release after landing safety fixes in application code; this issue tracks pytest in dev + CI + Docker split and phased test depth.
• Image size: keeping pytest in the dev group and excluding dev from the production poetry install keeps runtime image impact at ~0; installing pytest as a main dependency without excluding dev in Docker would add on the order of ~5–20 MB under site-packages (rough estimate).