Apache Pluto's 'Testsuite' is a very useful first test to see if a Portal supports basic JSR168 features.

The portlets available for download here can be used to test additional, perhaps less well specified, features. Different Portals may implement each of them in subtly different ways, which may impact on the way your portlets work.

In particular, several of them were developed specifically to see if the portlet messaging library would work with a given Portal.