This repository is a running example of how to configure a project for testing Babel transpiled ES6 JavaScript that uses ES6 module syntax, using Mocha, Istanbul, Sinon and Proxyquire without adding any dependency to whatever module bundler/loader is used for delivering the code to browsers.
I've tested this in node 6.x and 7.x. If you're using ES6 modules, then you probably also have a fairly modern node on your system(s).
$ npm install
$ npm test
# use nyc (Istanbul CLI) to create a coverage report
$ npm run coverage
------------|----------|----------|----------|----------|----------------|
File | % Stmts | % Branch | % Funcs | % Lines |Uncovered Lines |
------------|----------|----------|----------|----------|----------------|
All files | 50 | 100 | 50 | 50 | |
hello | 100 | 100 | 100 | 100 | |
hello.js | 100 | 100 | 100 | 100 | |
proxyquire | 0 | 100 | 0 | 0 | |
hi.js | 0 | 100 | 0 | 0 | 2 |
------------|----------|----------|----------|----------|----------------|