[FEATURE] Native support for TGs test environment

[Bibo-Joshi]

By now, TGs dedicated test environment is more prominently documented. Adding native support for it in PTB could be a desribale feature.

⚠️ Current status

This feature is currently not on any roadmap, since it doesn't seem to be widely used. If you would like for PTB to have this feature, please react with a 👍 to the comment. If we see a large number of requests, this issue will likely get put on a roadmap.

Edit: One can trick PTB into using the test env by setting token='<token>/test'. But this hack is not guaranteed to keep working in future versions of PTB …

Open Questions

We should check how the url returned by get_file behave, i.e. if they are still https://api.telegram.org/file/bot<Token>/… or if they are e.g. https://api.telegram.org/file/bot<token>/test/….

Implementation options

Just quickly listing two options that come to my mind

A test_env flag

That would work via ApplicationBuilder().token(…).test_env(True) or Bot(…, test_env=True) . This would be non-breaking. However, if may not play nicely with custom base_file_url depending on what we find out about file urls.

Allow custom insertion of token into base(_file)_url

That could either work by requesting the user to pass something like base_url = 'api.telegram.org/bot{token}/' (this would be a breaking change) or by allowing the user to pass a Callable[[str], str] that accepts the token and returns the (file_)url (this could be implemented in a non-breaking manner)

[Nickelza]

It's currently the only way to test topics without having 200 members in a test group

[harshil21]

It's currently the only way to test topics without having 200 members in a test group

As of Telegram 9.3 (Dec 30, 2022), we can now make a group of any size into forums.

[Bibo-Joshi]

For future reference: A first draft PR was already made in #3972 and if we ever decide to go ahead with this, a PR may possibly build up on that PR.