How to design a test case for an inter-class?

As the integration of object oriented system begins, the designing of test cases becomes difficult. Testing of collaborations among classes should start at this point. It can be accomplished by applying random and partitioning methods and also scenario based and behavioral testing.

Multiple class random test cases can be generated in following steps:
- Generate random test sequences from the list of class operations for each client class and these messages are sent to server classes.
- Collaborator class and the operation is determined for each message that is generated.
- The transmitted messages are determined for each operation in the server object.
- The next level of operations are determined for each of the messages.

A state diagram for a class is used to help in deriving a sequence of tests that exercises the dynamic behavior and the classes that are collaborated with it. The tests that are designed should achieve all state coverage. Every behavior for the class should be adequately exercised. In case of inter class test case design, multiple state diagrams are used to track the behavioral flow of the system.

A state diagram can be traversed in a breadth first manner. It implies that a test case exercises a single transition. When a new transition is to be tested only previously tested transitions are used.