test/test/fixtures/test-runner/custom_reporters/custom.js

Node.js 18's node:test, as an npm package

// https://github.com/nodejs/node/blob/9eb363a3e00dbba572756c7ed314273f17ea8e2e/test/fixtures/test-runner/custom_reporters/custom.js
const assert = require('assert')
const path = require('path')
module.exports = async function * customReporter (source) {
  const counters = {}
  for await (const event of source) {
    if (event.data.file) {
      assert.strictEqual(event.data.file, path.resolve(__dirname, '../reporters.js'))
    }
    counters[event.type] = (counters[event.type] ?? 0) + 1
  }
  yield 'custom.js '
  yield JSON.stringify(counters)
}