docs: list all opt-in test suites

[promiseeuler]

Context

While reviewing HFlow's contributor setup after cloning the repository, I noticed that CONTRIBUTING.md described two opt-in integration suites, while tests/test_storage.py contains a third live object-store suite gated by HFLOW_TEST_BUCKET_URL.

Change

• describe all three external dependencies: network access, Docker, and a writable object-store prefix
• add the runnable command for the live bucket suite to the existing opt-in test block

Closes #70.

Validation

• git diff --check — passed
• verified the command and environment-variable gate against TestLiveBucket in tests/test_storage.py
• lychee was not available locally; this change adds no Markdown links

Checklist

• I added or updated outcome-focused tests for changed business logic. (Not applicable: documentation only.)
• I updated documentation for changed behavior, flags, formats, or requirements.
• I ran uv run ruff check --fix, uv run ruff format, and uv run ty check. (Not applicable to this Markdown-only change; uv is not installed locally.)
• I ran the relevant pytest suite. (Not applicable: no runtime behavior changed.)
• I did not add recordings, generated media, credentials, private URLs, or runtime artifacts.
• I preserved stored-data compatibility.

[github-actions]

👋 Hi @promiseeuler — thank you so much for your first contribution to HFlow!

A maintainer will review your pull request as soon as possible. In the meantime:

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💡 Tip: one open pull request per contributor at a time. Issues with an assignee are taken; everything else is fair game.

We are excited to have you here and appreciate your help making the project better! 🙌

[kstonekuan]

Welcome, and thank you @promiseeuler. Merging.

You did the thing the issue asked and one thing it did not: the issue said "there are three", and you also rewrote the sentence to say why each one is opt-in (network, Docker, object-store prefix), which is the part that tells a reader whether they need to care. The example URL matching the form in tests/test_storage.py's own docstring is a nice touch.

What I validated:

• Exactly three env-gated suites exist: HFLOW_NETWORK_TESTS (tests/test_ffmpeg.py:262), HFLOW_DOCKER_TESTS (tests/test_runtime_integration.py:39), HFLOW_TEST_BUCKET_URL (tests/test_storage.py:372). Nothing is missing from your list and there is no fourth.
• Ran the lychee command for you, since you noted uv was not available locally: 10 links, 0 errors.
• Grepped for other places claiming "two" opt-in suites. None left, so this closes the whole issue rather than one instance of it.

Marking the checklist items "not applicable" with the reason, instead of ticking them, is exactly right for a Markdown-only change. Do keep doing that.

Two notes for your next one:

#107 was auto-closed by a bot, not by me, and no work is lost. We cap non-collaborators at one open pull request at a time so every one gets a real review. With this merged you can reopen #107 straight away and it will be reviewed on its merits. Sorry for the noise of finding that out by surprise.

Your #108 is a genuine bug and a good catch. test_env_override_wins hardcoding /usr/bin/ffmpeg while CONTRIBUTING.md lists macOS as supported is a real inconsistency, and your tmp_path fix is the right shape: the test only exercises precedence, so it does not need a real binary. I have labelled it and it is yours if you want it after #107.

One thing worth saying since you are three-for-three on finding real problems: the failures you listed in #107 (/usr/bin/ffmpeg, missing lzma, no drawtext filter) are worth their own issues rather than a footnote in a PR body. Two of the three are portability bugs in our test suite, not facts about your machine.