Currently, in CI, Parsoid/JS spins up a service using mockAPI.js as the MediaWiki API and runs the mocha/api.js suite.
For the purpose of the port, we have a patch which lets a local MediaWiki instance with the installed Parsoid/PHP extension also use mockAPI.js for DataAccess and then we can run the mocha/api.js test suite with a supplied PARSOID_URL (added in T221168).
Moving forward though, we probably want to move to whatever the MediaWiki action API is tested with and do away with mocha altogether.