The first level of documentation should be directly in the code, especially for the public interface method and classes that are exposed to the user. I suggest to use Javadocs for them. Another kind of documentation should be done with example tests which can serve as a template and explain all the possibilities of writing a test and using the test framework features. Additionally, we could provide an overview in the externally visible and easy to find OpenJDK Wiki page to summarize the most important points and links to the examples and/or other resource about the test framework.