The integration testing coverage in Seam in Action is covered very briefly for two main reasons:
A thorough discussion of testing belongs in a testing book
Testing in Seam is supported by a single test class, so it is very straightforward
The main reason for the terse coverage is to prove a point, that testing really is simple to do in Seam. What Seam focuses on is getting Seam bootstrapped in such a way that you can write your own tests (SeamTest, and also DBUnitSeamTest if you need it). While it's true that there is something to be said for trying demonstrating the various scenarios and styles of testing of testing Seam applications (because everyone has their own way about it), it's really a whole other topic that warrants a book on testing with a section on Seam.
In closing thoughts, Seam really isn't a testing framework. SeamTest is simple, straightforward and effective.