It is always the same, if you want to clean up a test database, you need to drop all tables from the schema.
I do this like that way:
select CONCAT(CONCAT('drop table "', object_name), '" cascade constraints;') from user_objects where object_type = 'TABLE';
Then you’ll get a nice list with all tables, copy and paste it, for example in your SQL Developer, run it and all Tables are dropped.
Easy peasy 🙂