added test for 'clean' argument passed to 'start_polling()' - #2002

Hi. Thanks for the PR.
TBH, I don't really understand, what's going on. IISC, What we would want to test is

Trying to test clean. Clean will cause all updates to be ignored. It does that by getting all updates and than calling get_updates() with the highest update_id. This results in all updates with a lower id to be discarded.

* On the first call of `get_updates()`, that returns a list of updates with ids

I mocked get_updates() to return a list of fake updates when called the 1 first time. The second time it's called we will pass an in update_id from the bootstrap ____clean function. We want to know what id that is and verify it's the 'highest'.

* Make sure that for every such id `i`, `get_updates()` is called with `offset=i`

bootstrap___clean doesn't behave like this. It just assumes that the updates are chronological and takes update_id from the last item in the list.

I don't really get, how self.update_id achieves that and what the "infinity loop protection" does

My logic is that if we pass 3 id's, and we know the highest id = 3 than we can validate clean by checking which update_id it will call get_updates() with the second time.

inf loop protection is something left over from debugging

If get_updates() behaviour changes, it won't be caught with this test. if we want to test for that we shouldn't mock get_updates().

… Could you try to make the code more intuitive to read? Descriptive namings and precise comments are helpful for that ;)

10-4

Thank you for your contribution :)