Currently the Reference Previews browser tests are all skipped on the CI. See [1]
There's a JS parameter checking if the tests should be skipped and that parameter takes into account the general feature availability and the beta feature status.[2]
Currently the feature is by default provided as beta feature so if the tests do not enable the beta feature manually in the user settings they are skipped.
[1] https://integration.wikimedia.org/ci/job/quibble-vendor-mysql-php72-selenium-docker/14818/console
[2] https://gerrit.wikimedia.org/g/mediawiki/extensions/Popups/+/edd18801ca4e18602c32f5df792d615e17e5a63e/includes/PopupsContext.php#134