test: add early-exit tests

[43081j]

These are copied from prettier. The following have been removed:

• show detailed usage with --help l
• show usage per option (e.g. --help tab-width)
• throw error when usage requested for unknown option (e.g. --help foo)

The following have been changed:

• throw error and show usage when called with no args
  • we do not currently show usage

cc @fabiospampinato

[fabiospampinato]

show detailed usage with --help l

Ok for simplicity let's not think about this now, especially as that doesn't seem to provide particularly interesting information for Prettier, it's 99% the same content that's in the help page.

But it has an interesting behavior, where for example they can show different help text for --color and --no-color, which is something we don't support at all anywhere, but also I'm not sure it's that useful.

I think it's fine to not implement this in v4, and if people complain I can add it back in the future.

show usage per option (e.g. --help tab-width)

Same as above.

throw error when usage requested for unknown option (e.g. --help foo)

yeah if that's not supported what would we throw an error for, I guess.

[fabiospampinato]

The following have been changed:

throw error and show usage when called with no args
we do not currently show usage

That seems fine, I don't know of another CLI that shows the help text in that scenario.

[fabiospampinato]

If you can rebase and update the tests about stderr it seems fine to merge this 👍

[43081j]

have rebased and fixed stuff up

but i think i lost commits you did as i didnt realise you pushed here

[fabiospampinato]

Thanks!

[fabiospampinato]

I added a couple of more text to make sure all 3 main flags are considered incompatible with each other, and also for some flags that are considered not supported anymore at the moment.