JUnit theory for hashCode/equals contract

Question

The following class serve as generic tester for equals/hashCode contract. It is a part of a home grown testing framework.

• What do you think about?
• Ho

Answer 1

One thing to consider: testing an object's conformance to the equals contract should involve instances of other types. In particular, problems are likely to appear with instances of a subclass or superclass. Joshua Bloch gives an excellent explanation of the related pitfalls in Effective Java (I'm reusing duffymo's link, so he should get credit for it) -- see the section under Transitivity involving the Point and ColorPoint classes.

True, your implementation doesn't prevent someone from writing a test that involves instances of a subclass, but because ObjectTest is a generic class it gives the impression that all data points should come from a single class (the class being tested). It might be better to remove the type parameter altogether. Just food for thought.