Node 20, and the test runner that ships with it

A test runner in the standard library, stable in 20, which covers a range of projects that had been reaching for a dependency out of habit.

import { test, describe } from 'node:test'
import assert from 'node:assert/strict'

describe('slugify', () => {
  test('lowercases and hyphenates', () => {
    assert.equal(slugify('Hello World'), 'hello-world')
  })
})

// $ node --test
// no config, no dependency, no transform

For a package of plain JavaScript utilities this is complete, and using it removed 41 transitive dependencies from one repository. What it does not have is a browser environment, module mocking, or snapshot testing, so anything rendering components stays where it is. The watch mode and the coverage flag arriving later made it usable rather than merely present.