`tests`: Provide a way to run tests with PTY stdout

[RenjiSann]

Some utils' behavior may change depending on the stdout().is_terminal() answer.
This is the case for ls which adapts its default quoting style depending on STDOUT being a TTY or not.

The issue is that from what I saw, the testing utilities do not provide any way to test these TTY behaviors.

Maybe we could adapt the utilities to offer such verifications.
A straighforward way to go would be to use the pty_process crate.

[cre4ture]

I was implementing something like this for the "nohup" tests. Its still pending as PR: #5858

I was testing multiple different external crates. Somehow I was falling back to implement it manually.
But this decision was based on a mistake that I did myself and only recognised later on.

I think if we decide to have it as part of the testing utilities then it makes sense to investigate again and a bit deeper. Especially because there are actually multiple crates that provides a similar functionality:

pty-process = { version = "0.4.0", features = ["async"] }
fake-tty = "0.3.1"
tty-spawn = "0.3.1"
ptyprocess = "0.4.1
portable-pty = "0.8.1"

Was there a special reason why you suggest pty-process?

I did a very first rougth test with all of them and currently I think that "ptyprocess" (without the dash) is probably a good candidate as it seems to be easy to use and connects well with the std::process::Command.

[cre4ture]

update: After some testing, I have the feeling that all of the crates have some issue such that we can't directly use it.
Some even come from a time where the rustlib probably didn't provide much. But this is different today.
Such that I think we should try to make our own implementation similar as I did already. This works fine and is much less code than the implementation of any of the crates.

There is only on special thing to mention: portable-pty provides a implementation even for windows. I will investigate a bit more into that to see if we can also support even windows there.

[cre4ture]

the windows implementation for a pty in the rustlib is appartently not a new topic:
Tracking Issue for windows_process_extensions_raw_attribute
Add ability to spawn Windows process with Proc Thread Attributes

I think the windows implementation is not urgend and thus we should wait for the rustlib being extened to support it with the std::Command.

[cre4ture]

let me know what you think from proposal #5869

[RenjiSann]

let me know what you think from proposal #5869

Thank you !
The reason I only proposed the pty-process crate was that it felt similar to the way I we handle commands here.
However, the more I investigated, the more I realized I was missing knowledge and context about the deep functioning of PTYs.
Also I think I am not fluent enough in Rust yet to understand your whole PR, so not surprisingly, I wouldn't have proposed something better (although I keep hope in becoming better someday as I understand a bit of it).

Anyway, from what I read and understood, that's exactly how I imagined it.
👍 Thank you !

[RenjiSann]

Fixed by #5869