test_runner: enable in-source testing

[debadree25]

Just opening a draft PR to ask for feedback plus seek some help, have been trying implement in-source testing as per the linked issue, and would like to know if

a) This is the correct way to make the change
b) Also it seems that --test option value is not getting recognized somehow when using it within lib/internal/modules/esm/initialize_import_meta.js which is quite weird if anyone can explain this would be very helpful!!

Also most importantly would need discussion on whether this feature even is acceptable, the discussion on the original issue stopped some time back so hoping this one can continue the conversation

Fixes: #45771

[nodejs-github-bot]

Review requested:

• @nodejs/loaders
• @nodejs/modules

[debadree25]

cc @MoLow

[debadree25]

Ok have been able to work around the limitation of --test not coming for some reason with a new flag --test-in-source so something like

import assert from 'node:assert';
if (import.meta.test) {
  const { describe, it } = import.meta.test;
  describe('Test Suite', () => {
    it('Test Something', () => {
      assert.ok(true);
    });
  });
}

is working with node --test-in-source test.mjs

will try to work on tests now

[MoLow]

as stated here, the test runner is supposed to be lean and minimal - meaning it should include features that address the common testing use cases.
I am not convinced that this feature will be broadly adopted by node projects since:

1. this is a personal opinion but I consider in-source testing to be an anti-pattern for the majority of use-cases
2. it is ESM only, which is not (yet?) the majority of projects. if we want such a feature it should support both ESM and CJS

[debadree25]

Ahh understood I guess will keep it closed for now, will reopen if there is significant interest

[cjihrig]

I think it's also worth noting that (if I understand the feature request correctly) this can already be done using a conditional + require() or dynamic import(). One possible example:

if (process.env.NODE_ENV === 'test') {
  const test = require('node:test');
  // test things
}