ClassFormatError using JMockit with EMMA

I am trying to use EMMA to measure coverage of some JUnit tests that use JMockit. But when I try to run the JMockit tests after instrumenting with EMMA, about a quarter of the tests fail with the following error:

com.logstorage.engine.sensor.SensorManagerTest.setUpBeforeClass(SensorManagerTest.java:98)
    java.lang.ClassFormatError
    at sun.instrument.InstrumentationImpl.redefineClasses0(Native Method)
    at sun.instrument.InstrumentationImpl.redefineClasses(InstrumentationImpl.java:150)
    at mockit.internal.RedefinitionEngine.redefineMethods(RedefinitionEngine.java:152)
    at mockit.internal.RedefinitionEngine.redefineMethods(RedefinitionEngine.java:139)
    at mockit.internal.RedefinitionEngine.redefineMethods(RedefinitionEngine.java:73)
    at mockit.Mockit.setUpMock(Mockit.java:235)
    at com.myapp.MyTest.setUpBeforeClass(MyTest.java:98)

I can't see any pattern as to which tests fail and which don't. I guess this is just a bug in JMockit, but does anybody know a workaround?

I found a very similar question called "Getting ClassFormatError with EMMA?" but the solution doesn't work for me (I'm not using any reentrant=true mock methods). Any other ideas?

Thanks in advance.

Solution

I have been running into the same problem - this seems to have fixed it for me and hopefully will help anybody else as well.

If you're running this through ant, make sure you don't have vars in your javac target's debuglevel argument. The following target will cause the error.

<javac srcdir="${src}" destdir="${bin}" debug="on" debuglevel="lines,source,vars" nowarn="true" />

Change it to:

<javac srcdir="${src}" destdir="${bin}" debug="on" debuglevel="lines,source" nowarn="true">

This is probably a JMockit bug - very subtle and annyoing to find out.