Is it possible to use java.lang.instrument.Instrumentation in JUnit tests?

Question

Is it possible to use java.lang.instrument.Instrumentation in JUnit tests? I use mockrunner to simulate a servlet and want to measure the size of objects stored in a session

Answer 1

Yes, it is possible, but not very simple.

The problem with using java.lang.instrument.Instrumentation is that you ALWAYS have to use the JVM agent. A good introduction to JVM agents is available at http://www.javabeat.net/2012/06/introduction-to-java-agents/ .

However, since your unit tests also run in jvm, you can specify an agent as a JVM argument.

A JVM agent for reporting on the state of memory that you want to make and ready for packaging is available at https://github.com/jbellis/jamm . You can build it with either Maven or Ant. To use it, you create it and then pass the following as a jvm argument when you run the unit test or unit test suite:

-javaagent:<path to>/jamm.jar 

As part of unit tests, you can create an instance of MemoryMeter and use it:

 MemoryMeter meter = new MemoryMeter(); meter.measure(object); meter.measureDeep(object); meter.countChildren(object); 

Answer 2

I used jmockit in unit testing, which could mock anything. Extending this, java.lang.instrument.Instrumentation should also work.