Different transaction log for database/schema

Hello,

I would like kindly ask for an advice whether and how the transaction log
behavior could be configured.

I would like to have possibility to differentiate transaction logs for two
databases or schema. I would need such configuration for my testing
environment where I need to run simultaneously different tests using
transactions. And I need to separate those tests for being sure that they do
not interfere with each other. I'm using XA transactions in Java. 

Is there some way how to reach such behavior? Or is it possible to define
where to store prepared transaction for a current session?

Thank you for any hint or explanation how the things work in PostgreSQL

Regards
Ondrej Chaloupka