Both Player itself and addons as whole are subject to specific testing and building process. To be more precise, either of them can be builded without successfully passing test phase. Player itself testing is standard Java unit testing. When it comes to Addons it needs some workspace preparing from developers.
Make a copy of build-example.properties file and name it build.properties. Next change path to Google Web Toolkit SDK in newly created file accordingly to your local setup.
java -jar addons/tools/JsTestDriver.jar --port 9876
When server is up and running you can open your browser and go to the following URL:
Type ant in command line to run defaul build target which includes testing all of Player components. After successful build you are ready to work with Player!