Allow faking a terminal for testing

[casey]

Thanks for this! I'm using it a command runner[0] to figure out when to produce colored error messages and it works great.

It would be great if I could somehow fool atty into thinking that a stream is a terminal for testing, so that I can make sure that error messages are being formatted correctly when a terminal is attached.

[0] https://github.com/casey/just

[casey]

Actually, I'm not entirely certain this is so useful. I was able to relatively cleanly add testing to my own project, so I don't have a strong use case for it. Other projects that use atty might be structured differently and thus benefit from the ability to mock atty, but not mine.

[softprops]

Nice. I'll leave this open in case you need it. Also neat project!

[hayd]

@casey how did you do this in just?

This might also be useful for #15.

[casey]

Hmm, it's been a while since I wrote the tests. I think that I had an option to force color, regardless of if we were printing to a terminal, so if I wanted to test formatting I could set that option to be true.

[hayd]

We have something like:

fn permission_prompt(message: String) -> DenoResult<()> {
  if !atty::is(atty::Stream::Stdin) || !atty::is(atty::Stream::Stderr) { return Err(permission_denied()) };
  eprint!("{} Grant? yN", message);
  ...  // more stuff

What maybe you'd want to do is refactor to use dependency injection instead? https://stackoverflow.com/a/28370712/1240268 but then you not able to get an atty::Stream.

[hayd]

Okay, here's one way to fake TTYs in stdin, stdout and stderr:
https://stackoverflow.com/a/52954716/1240268
https://gist.github.com/hayd/4f46a68fc697ba8888a7b517a414583e