FireAcademy.io also provides a testnet10 instance for testing. It is equipped with the latest version of Leaflet.
Leaflet (testnet10) can be accessed at https://kraken.fireacademy.io/leaflet-testnet10/ or https://kraken.fireacademy.io/{api-key}/leaflet-testnet10/. Each request has a different, static cost - please see this page for more information, including a list of the allowed endpoints.