How should one unit test the hashCode-equals contract?

Question

In a nutshell, the hashCode contract, according to Java\'s object.hashCode():

1. The hash code shouldn\'t change unless something affecting equals() changes

Answer 1

It's worth using the junit addons for this. Check out the class EqualsHashCodeTestCase http://junit-addons.sourceforge.net/ you can extend this and implement createInstance and createNotEqualInstance, this will check the equals and hashCode methods are correct.