Licensing of Oracle Standard One multiple homes
The correct answer for licensing questions is: contact your oracle sales representative.

With Oracle you license cpu's. If your test and prod run on the same cpu's, they don't need a new license. As long as it all runs on the same cpu's, it does not matter if you have multiple databases (and instances) or run it all in one single database. Normally we don't mix test and prod in the same database so at least make sure to create separate databases for test and prod.

If you run this on the same machine, it could be wise to run test using a test account and prod database using a prod account. This also requires 2 separate ORACLE_HOME's on that single machine but this does give you some control about the separation of your environments.