Add a TestConsole

[morgen-peschke]

Implements suggestion in #4393

[djspiewak]

Is there a reason to have a separate logsRef? It seems redundant given that we have stderr/stdout

[djspiewak]

I'm kind of surprised at this structure and would have expected something more like a Queue. Wouldn't it be more useful to allow users to build tests which supply input more ergonomically?

[morgen-peschke]

I'm not sure I understand what specifically you're asking about.

If you're asking about the API, the users use TestConsole#write and TestConsole#writeln to supply input, they don't need to interact with the internal bits.

If you're asking about the structure of the internal bits, if this were implemented with a Queue, it would still need something like TestStdInState to track the partial lines, so it would only really get rid of the Semaphore.

Since I had to work with TestStdInState anyway, it was simpler to track the requests locally instead of delegating that to a Queue (especially since only one state needs that functionality anyway).

[morgen-peschke]

I've separated out the algebras that control stdIn and inspect the state of things to hopefully clarify how the user would build tests and supply input.

[iRevive]

Would it make sense to shape a test console around an ADT? We have this implementation in otel4s: https://github.com/typelevel/otel4s/blob/4b5f51093e3bb2fbb20914f901a5752a88d8e26c/sdk/common/shared/src/test/scala/org/typelevel/otel4s/sdk/test/InMemoryConsole.scala#L28

The ADT offers enough flexibility to test operations.

P. S. To be fair, it doesn't support read operations, but it can be implemented with a separate read queue.

[iRevive]

On the other hand, since TestConsole covers different scenarios, it might be worth exploring two different implementations.

[morgen-peschke]

Is there a reason to have a separate logsRef? It seems redundant given that we have stderr/stdout

Those are for capturing meta information that's useful when tests fail, like that there was X amount left in the buffer at close, the exact sequence of reads and writes, etc.

For context: I initially wrote this as a local helper when writing tests for typelevel/log4cats#912, and the additional context was really helpful for debugging those tests.

[morgen-peschke]

Would it make sense to shape a test console around an ADT?

I think the main reason I went with a design that provided the full output of each stream, rather than an ADT tracking each operation, is that it would encourage writing tests using it which would be less sensitive to internal implementation changes.

It feels like a smell if we encourage users to write tests that care if there's a switch under the hood from console.println(fooNel.mkString_("\n")) to fooNel.traverse_(console.println(_)), since the observable behavior is the same.