The quality of the Unit-Tests can be in general projected to the quality of the production code. In source code reviews, I look first at the Unit-Tests and try to find out, how the code was intended to be used.
I was also curious, how the JPA layer was tested by different application server vendors and reviewed glassfish and jboss code. Fortunately, you can access both source branches directly from the browser
I'm curious about your results - you can use the comments in my blog to document these :-).