OGM-233 OGM is not polymorphic 

https://hibernate.onjira.com/browse/OGM-233

The discriminator is created only if it's needed.
Discriinator formulas are not supported (should I open a JIRA for this?)

The single table strategy is the only one supported at the moment but I don't know how to check that the column is actually created with a unit test. Any suggestion?