Custom JVM property

I am trying to figure out how to add a custom jvm property that my Java application can read with code similar to the following:

String test= System.getProperty("test");

The only thing that I have found on http://help.sap.com is a reference to a instance.properties file located in \usr\sap\ET1\JC00\j2ee\cluster. Is that where I should add my property? If so is the format something like:

test=somevalue

Thanks,

Steve