In contrast to the explosion of activity in object-oriented design and programming, little attention has been given to object testing. We present a novel approach to automated testing designed especially for collection classes. In the ClassBench methodology, a testgraph partially models the states and transitions of the Class-Under-Test (CUT) state/transition graph. To determine the expected behavior for the test cases generated from the testgraph, the tester develops an oracle class, providing essentially the same operations as the CUT but supporting only the testgraph states and transitions. Surprisingly thorough testing is achievable with simple testgraphs and oracles. The ClassBench framework supports the tester by providing a testgraph editor, automated testgraph traversal, and a variety of utility classes. Test suites can be easily configured for regression testing-where many test cases are run-and debugging-where a few test cases are selected to isolate the bug. We present the ClassBench methodology and framework in detail, illustrated on both simple examples and on test suites from commercial collection class libraries. Β©1997 John Wiley & Sons, Ltd.