Document why `node:test` exists

Affected URL(s)

https://nodejs.org/api/test.html

Description of the problem

Background

The core module node:test was proposed in https://github.com/nodejs/node/issues/40954 and shipped at Experimental stability in 18.0.0 via https://github.com/nodejs/node/pull/42325. Dozens of people expressed support for the idea via 👍 reactions and written comments. The sentiment of commenters toward the feature is overwhelmingly supportive.

Problem

TL;DR the questions asked in https://github.com/nodejs/node/issues/40954#issuecomment-1037512376 seem unanswered, reducing the likelihood that node:test becomes adopted.

It's unclear what problems the project aims to solve by including a test runner in core.

...or should I say—given the broad support shown by participants in https://github.com/nodejs/node/issues/40954 —that they're unclear to me. 😕

• If it's relevant, my background: I'm primarily a maintainer of Node.js applications, ~5 years of experience doing so, and am not a maintainer of any OSS.
• I'm unsure how "should X go in core?" questions are usually settled, or if there are heuristics that exist in docs somewhere or in the heads of regular contributors. I went looking and found https://github.com/nodejs/node/blob/68fb0bf553e2af3e0b61733d29e1e9ba7f73d9b2/doc/contributing/pull-requests.md#accept-that-there-are-different-opinions-about-what-belongs-in-nodejs, which doesn't address the question so much as COC concerns at the periphery of the question. The couple “sufficient to put a thing in core” criteria it does identify aren’t met by a testing framework.

@bcomnes had a comment here - https://github.com/nodejs/node/issues/40954#issuecomment-1037512376 - that resonated very much with me: It distilled and synthesized a lot of rough ideas that commenters had submitted up to that point. IMO his comment effectively highlights the variety of goals that people might have for the module. It seems to me that the questions he raised remain unanswered.

cc @nodejs/test_runner (which I saw referenced in https://github.com/nodejs/TSC/issues/1194#issuecomment-1088280424 as a recently formed team)

meta note: My framing of this as a docs request might not be the best. If this is more suited as a Discussion or other type of issue, please let me know. Thanks.

Start with the affected nodejs.org/api/test.html page, then read the linked proposal issue and its referenced comment, along with doc/contributing/pull-requests.md. Confirm the project’s agreed rationale and goals for node:test before changing the documentation; done means the page clearly explains why the module exists and addresses the open questions.