The latest DrJava source code does not appear to be the latest in the Git repository. I noticed as the latest build (drjava-20190813-220051) has a Code Coverage button that is not present in the latest version of MainFrame.java in the git repository.
Feel free to reject this if the project is abandoned, but I was trying to trace exactly what was happening with the Code Coverage tool and why it consistently crashes for me.
I think (but am not sure; I haven't been a maintainer in ~15 years) that it is now at GitHub.
There is a more recent build under the name drjava.jar at https://www.cs.rice.edu/~javaplt/drjavarice/drjava.jar
that fixes a bug we encountered with jacoco code coverage. I am using a Windows 10 laptop as my primary machine which does not interoperate very well with github. I will try to push our local repository to github shortly. In the meantime, I recommend the build shown above. DrJava is little used at Rice these days.