Running org.hibernate.testing.junit4.BaseNonConfigCoreFunctionalTestCase from Hibernate ORM test suite of version 5.3.20 on MySQL 8.0 database results in a HibernateException:
Caused by: org.hibernate.HibernateException: Connection pool is no longer active
Note: the issue is not present in the latest ORM version (5.5.0), filing this JIRA as a known issue for QE Hibernate ORM 5.3.20 testing.