Summary: The java.debugging project contains two main test sets:
Hot Code Replace (HCR) - Late Attach
This test set runs number of tests randomly, repeatedly, and concurrently to put the VM and JIT under load for five minutes. We then late-attach a java agent which performs HCR on the String class for the duration of the workload.
The full HCR test readme can be found here.
Java Debugging Interface (JDI)
JDI is an api which allows connection via a debugger to low level debugging tools, such as breakpoints and field watching. The debugger creates a connection to the target VM allowing user-created trace and debugging to be set and trigger user code.
This test set is broken down into multiple sub-tests, each of which can be run separately or together (serially). Each sub-test tests a different aspect of the JDI.
The full JDI test readme can be found here