Fix parallel feature: disable parallel automatically/ add command line option

[stoicchild8910]

Requirements

• Filling out the template is required. Any pull request that does not include enough information to be reviewed in a timely manner may be closed at the maintainers' discretion.
• All new code requires tests to ensure against regressions.

Description of the Change

This PR comes from the idea #4322
AS-IS
[single run]

[parallel run]

(1) fix parallel feature : When running a single file, disable parallel mode automatically.

If we run only a single file in parallel mode, it is much slower.
So I added a feature to automate swap from parallel mode to single mode when we're running a single file.

(2) Added Command Line Option: added an option to FORCE PARALLEL MODE in (1) situation

Alternate Designs

Why should this be in core?

Benefits

When running a single file, Mocha automatically run in a faster way.

Possible Drawbacks

There must be a way to force parallel mode when running a single file if needed.

Applicable issues

[jsf-clabot]

All committers have signed the CLA.

[stoicchild8910]

I'm working on failed test cases!

[stoicchild8910]

I am still working on test cases and PRs.

[boneskull]

Thanks for the PR!

In general, I agree with this--Mocha should not run in parallel if there is only a single file, and we need a way to force it to run in parallel. This will affect many of our tests, as you have probably discovered. A way to address this is to detect --parallel in the arguments (see test/integration/helpers.js) and append --force-parallel to it. I would prefer the option is called --force-parallel, not --parallel-force.

[boneskull]

I am unsure if this would be a breaking change. Ideally, it would not have any impact on consumers, but... you never know.
@mochajs/core thoughts?

[boneskull]

Please mark this PR as "ready" when the tests are passing

[stoicchild8910]

Please mark this PR as "ready" when the tests are passing
Thank you for your opinion!

I also don't think many customers would run a single file in parallel option.
And that's the point where I thought to predict running time and automatize running mode.
For example we can test on many different files and how much time it needs to run -> if we have our standard we can automize running mode.
This is just my opinion!

And I will do mark PR when test passed.

[boneskull]

@stoicchild8910

I also don't think many customers would run a single file in parallel option.

right, consumers may not, but Mocha needs to do so in order to efficiently test parallel mode. so this is why I'd want --force-parallel

[JoshuaKGoldberg]

👋 coming back to this @stoicchild8910, are you still interested in working on this PR? As of #5027 there are again maintainers who can review it now. No worries if you no longer have time - but if you do that'd be great!