I wanted to use the helper functions in zeppelin-solidity/test/helpers/ in my project, but had a hard time importing them. They’re exported using ES2015 module syntax, so I had to add babel-register as a dependency and run:

require('babel-register')({
    ignore: /node_modules\/(?!zeppelin-solidity)/
});

It would be easier to add as a dependency in other projects if they were bundled and transformed to CommonJS