Enable tests to validate typings

[MIchaelMainer]

Tests were never completed. It appears we were blocked on using the ES6 module in Node. See Babel unexpected token import when running mocha tests.

We may want to consider adding test cases with tsd.

AB#7042

[MIchaelMainer]

We published typings to npm before we published to DefinatelyTyped. DefinatelyTyped PR validation caught an error. We should use the same (or similar) validation on our PRs so we catch errors like what was caught by the DefinatelyTyped.