test_runner: disable highWatermark on TestsStream

[cjihrig]

The default highWatermark of 16 on the TestsStream class can have a substantial impact on reporting performance. This commit sets the TestsStream highWatermark to a very large value and lets the destination streams (which are more likely to have meaningful highWatermarks) handle backpressure.

To test this, I ran the following code:

'use strict';
const { describe, it } = require('node:test');

for (let i = 0; i < 100; ++i) {
  describe(`suite ${i + 1}`, () => {
    for (let j = 0; j < 100; ++j) {
      it(`test ${i + 1}-${j + 1}`, () => {});
    }
  });
}

Running the command time ./node test.js on my machine before and after this change yielded:

Before this change:

• With --test: 2.12 seconds
• Without --test: 1.43 seconds

After this change:

• With --test: 0.94 seconds
• Without --test: 0.42 seconds

For reference, mocha (time ./node ./node_modules/.bin/mocha test.js, with the node:test import removed) yielded 0.95 seconds.

[nodejs-github-bot]

Review requested:

• @nodejs/test_runner

[MoLow]

amazing

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/58013/

[nodejs-github-bot]

Landed in 2c024cd