sealed ZHub - problem with test instance

[PawelJ-PL]

Hi,

I've found a pretty fresh PR #4925 (already merged). This approach makes unit tests more complicated. Normally I would create my custom implementation of ZHub for the test which would use Ref to collect published messages (to verify them later in the test). But since this change it's impossible.
Now I have to implement not nice solution like:

 for {
      internalMessages    <- Ref.make[List[InternalMessage]](List.empty)
      internalTopic       <- Hub.bounded[InternalMessage](16)
      internalMessageCollector =
        ZStream.fromHub(internalTopic).run(ZSink.foreach(message => internalMessages.update(prev => prev :+ message)))
      serviceQuery = UsersService.createUser(newUserReq)
      user                <- internalMessageCollector.raceEither(serviceQuery).rightOrFail(new RuntimeException("Stream finished to soon"))
      sentMessages        <- internalMessages.get
    } yield assert(sentMessages)(hasSameElements(List(InternalMessage.UserRegistered(...)

I think, It may be worth considering treating ZHub as a regular trait instead of sealed

[adamgfraser]

@PawelJ-PL ZHub was a sealed trait prior to that PR being merged so you wouldn't have been able to extend it even then. You can use contramapM to perform an effect like writing to a Ref for each value that is published to the hub. I am 👎 on removing the seal as I don't think the hub is meant to be extended by third party code and it creates binary compatibility issues.

[PawelJ-PL]

Solution with contramapN will work as fine in tests as a custom implementation based on Ref.

[adamgfraser]

@PawelJ-PL Awesome! Are we good to close this then? Thanks for trying out ZHub and for raising this.

[PawelJ-PL]

Yes, I'll close issue. Thank you for suggestion.