I got this from a local build of http://hg.openjdk.java.net/jdk/jdk/rev/ae4295a6a01e.

java.lang.Error: Unexpected thread info line: at TestThreadDumpClassInitMonitor$Target$1.run(TestThreadDumpClassInitMonitor.java:91)
at TestThreadDumpClassInitMonitor.main(TestThreadDumpClassInitMonitor.java:153)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:569)
at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:127)
at java.base/java.lang.Thread.run(Thread.java:835)

In my case, the test fails product build, but passes with fastdebug build. However, the stack for the thread that the test complains about is identical in both builds. So this is probably caused by a bug in the test:

"TestThread" #12 prio=5 os_prio=0 cpu=0.38ms elapsed=0.62s tid=0x00007f5914019000 nid=0x665f in Object.wait() [0x00007f59497d0000]
   java.lang.Thread.State: RUNNABLE
at TestThreadDumpClassInitMonitor$Target$1.run(TestThreadDumpClassInitMonitor.java:91)
- waiting on the Class initialization monitor for TestThreadDumpClassInitMonitor$Target