This Javascript implementation uses Mocha, Chai, and supports ES6.
npm install
npm test
npm run test:watch
NOTE: When using IntelliJ IDEA, import { expect } from 'chai' will likely show up as an unrecognized import.
See https://intellij-support.jetbrains.com/hc/en-us/community/posts/115000357324-Get-rid-of-Unresolved-function-method-variable-warning-in-Jest-test-files Downloading the chai Javascript library (Preferences->Languages & Frameworks->Javascript->Libraries ->Download...) fixed this problem.
Creating a run config in IDEA:
Under Run/Debug Configurations, add a Mocha test. Name it. User interface: BDD Extra Mocha options: --require @babel/register --require @babel/polyfill --watch --reporter min Test directory: point to the src directory and include subdirectories.