>> How do you run automated tests for applications which depend on state of an Oracle database/schema?
Oracle Multitenant (no need for option and this may be done with free Oracle XE) can flashback a Pluggable DataBase very fast.
Of course, people would like to use the same technology for all components. But whether OS containers are good for the application server, it is not the right choice for a database instance (many processes with shared memory and persistent storage). With Multitenant, the CDB runs those processes and memory and can create/drop/flashback database containers which are the PDBs. Think about PDBs for data in the same ways as docker containers for software.