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Is there anything out there (for Java specifically) that allow you to automatically test the behavior of an interface? As an example, let's say I have a bunch of tests for the Comparable interface, that should apply to anything that implements Comparable. What I'd like is to be able to include "ComparableTests" automatically in the test fixtures for any of my classes which implement Comparable. Bonus points if this would work with generic interfaces.
I know the .NET framework mbUnit has something similar, and when you're using something like TestNG's generator functions you could set up a test fixture for Comparable and have the generator create an instance of each of your classes that implement Comparable. But I'd rather have it be automatic, and located at the test fixture for each of my classes (since I'll already have them around for testing other parts of that class).
Clarification: I could definitely build something like this. I was asking if there was anything out there that already enabled this.
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To declare a class that implements an interface, you include an implements clause in the class declaration. Your class can implement more than one interface, so the implements keyword is followed by a comma-separated list of the interfaces implemented by the class.
Every class does implement an interface (i.e. contract) insofar as it provides a non-private API. Whether you should choose to represent the interface separately as a Java interface depends on whether the implementation is "a concept that varies".
Record Business Rules as Tests adopts a different strategy to developing tests which focuses on exercising business rules. This is fine if the components to be tested are the ones that implement the business logic. For most other components, Test the Interface, Not the Implementation will likely be more appropriate.
You can use an abstract test case to test an interface with common tests independent of implementation, and then generate concrete instances of the test case for each implementation of the interface.
Based on your last paragraph, what you're trying to do is inject some 'extra methods' into unit testing since you're already testing a specific class. I do not know of a testing harness that allows you to attach tests based on the hierarchy of a class.
However, with your own suggestion of using TestNG for building something similar, I think you might be very close. You could very well incorporate some base code that adds your class to a list of 'default test classes', which are in turn tested if they implement a specific interface.
Still, regarding the general case, I think you're out of luck, since the Java type system is one-way, you can only (easily) find out what interfaces a class implements, not the other way around. Furthermore, the problem is 'where to stop looking': if you have a test that checks all your comparable implementers, do you want it to check the validity of String's one too, since that is in your Java environment?
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Try this http://www.xmlizer.biz/java/classloader/ClassList.java
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