chore: run tests through npm test

This PR is more a question about different ways of running tests (although merging this one wouldn't hurt for now). It looks like migration from Grunt to gulp made the `gulp test` task disappear. Not sure what is the strategy here but I would love to be able to type 'gulp'  (or `gulp build`) to execute all the build steps with test. 

Would be happy to craft a PR based on your input!