The tests fail when run with --enable-preview

FATAL ERROR in native method: Error in event_storage_add: Exception in jni NewWeakGlobalRef

Adding some diagnostic info we see:

Exception in thread "MainThread" java.lang.IdentityException: java.lang.Byte is not an identity class
at java.base/java.lang.invoke.MemberName.hashCode(MemberName.java:735)
at java.base/java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:951)
at java.base/java.lang.invoke.MethodHandles$Lookup.linkMethodHandleConstant(MethodHandles.java:3986)
at java.base/java.lang.invoke.MethodHandleNatives.linkMethodHandleConstant(MethodHandleNatives.java:606)
at MyPackage.HeapMonitorVMEventsTest.compareSampledAndVM(HeapMonitorVMEventsTest.java:105)
at MyPackage.HeapMonitorVMEventsTest.main(HeapMonitorVMEventsTest.java:122)

So the test is now incompatible with preview mode because Byte (and perhaps others) is now a value class and so can't be weakly-referenced from the native code.