For JS stuff Coming from Tap/Tape and just recently switched to AVA github.com/sindresorhus/ava It's super fast because it executes tests in parallel. It supports Tap protocol output which allows me to use my test reporters I am familiar with.
For testing React stuff I use shallow rendering facebook.github.io/react/docs/test-utils.html Comparing a string is pretty easy. No need for any browser/headless/webdriver/etc
AVA + ShallowRendering = super fast and good DX (developer experience)