Add the Quartz dispatcher to your components.xml? If you don't add it, your won't work anyway, no just the tests.
I have <async:quartz-dispatcher /> in my component.xml.
My app works well, the problem is only with tests.
Maybe your tests are seeing a different components.xml? Check your test classpath, etc. I have SeamTests running with <async:quartz-dispatcher />, so it should work. I don't use @IntervalCron though.