From DeveloperWorks, Taking component testing to the next level in WebSphere Integration Developer
Test case support, a new feature of WebSphere Integration Developer V6.1, lets you create a test suite, a collection of test cases. The test client allows you to test each component in
isolation or as part of the whole module, or system of modules. You can run the suites of test cases at any time to show you whether your latest changes cause tests to fail.
Written by my ex-colleagues on the Integration Test Client Team so naturally it must be one of the best articles on developerWorks.