Liskov's principle tells us that for certain protocols, it would be possible to generate test code that exercise this functionality, matter of fact isn't there a test out there that checks if equals and hashcode are correct?

What about baseing it on interfaces... yes better yet aspects!

Yes, Gargoyle GSBase http://gsbase.sourceforge.net/

http://www.visioncodified.com/

http://www.junitdoclet.org/features.html

and

http://www-106.ibm.com/developerworks/java/library/j-aspectj2/?open&l=007,t=gr

also use case generation and verification against spec. see jadvise

combine with Refactoring