I bumped the library to 1.0.0-beta.0 and ran COVERAGE=true ember test, it runs successfully without any errors (no babel issues). However, I do not see the coverage directory being created.

My coverage.js has

module.exports = {
  reporters: ['lcov', 'html'],
  useBabelInstrumenter: true
};

It is located in the path <addon>/tests/dummy/config/coverage.js.

I ran it on a mac and also on windows 10, the coverage directory does not get created.
Please let me know if you need more information.