The only issue I am encountering is a NPE with the ESTestCase
This issue was fixed upstream. Which version of ES are you developing against?
Since every good developer writes test, I decided to use the embedded Derby database for integration tests. What a nightmare in terms of security!
Instead of launching a test instance in memory (where you must then give your plugin all permissions needed for testing), we recommend creating a test fixture. See, for example, how the hdfs test fixture is used to test against hdfs.