Despite being optimized for Oracle RDBS and driver, UCP is meant to be a general porpouse JDBC connection pool and generally works well with non-Oracle JDBC drivers. HSQLDB is a lightweight SQL embedded database very useful for development or testing. However UCP and HSQLDB don't get on very well toghether.
The problem is that the JDBC data source org.hsqldb.jdbc.JDBCDataSource maps setUrl, setURL, setDatabase and setDatabaseName on the same internal field url. At the same time UCP when initializing its connectionFactory calls by reflection both setURL and setDatabaseName in this order. The result is that on JDBCDataSource the url is overwritten by the databaseName, which is usually left null, so the url ends up being null making it impossible for the data source to connect to the database.
You can work around this by setting databaseName instead of URL, but this is counterintuitive and awkward.
Maybe UCP should refrain from setting databaseName to a null or empty string? Of course one could also speculate that HSQLDB should reconsider mapping such etherogeneous property names on the very same field, but this is for another forum.