add test suite

any advice or pull requests in relation to adding a test suite to this library are more than welcome, and would be appreciated.

because its dependent on the DOM being present, it will likely require a headless browser.

Start by reviewing the JavaScript library and its DOM-dependent behavior; the issue names no existing test files or entry points. Investigate a headless-browser setup and define the required test scope with maintainers. Done means the library has a usable test suite that runs against a present DOM.

Written by the indexing model from the issue text.