Observed in recent jdk 10 Mach 5 testing:

Test output:
ACTION: main -- Failed. Execution failed: `main' threw exception: java.lang.NoClassDefFoundError: jdk/test/lib/JDKToolFinder
REASON: User specified action: run main/othervm ModuleName
TIME: 1.425 seconds
messages:
command: main ModuleName
reason: User specified action: run main/othervm ModuleName
Mode: othervm [/othervm specified]
Additional options from @modules: --add-modules java.base,java.security.jgss,jdk.security.auth,jdk.security.jgss --add-exports java.base/jdk.internal.misc=ALL-UNNAMED --add-exports java.base/sun.security.util=ALL-UNNAMED --add-exports java.security.jgss/sun.security.jgss=ALL-UNNAMED --add-exports java.security.jgss/sun.security.krb5=ALL-UNNAMED --add-opens java.security.jgss/sun.security.krb5=ALL-UNNAMED --add-exports java.security.jgss/sun.security.krb5.internal=ALL-UNNAMED --add-opens java.security.jgss/sun.security.krb5.internal=ALL-UNNAMED --add-exports java.security.jgss/sun.security.krb5.internal.ccache=ALL-UNNAMED --add-exports java.security.jgss/sun.security.krb5.internal.rcache=ALL-UNNAMED --add-exports java.security.jgss/sun.security.krb5.internal.crypto=ALL-UNNAMED --add-exports java.security.jgss/sun.security.krb5.internal.ktab=ALL-UNNAMED
elapsed time (seconds): 1.425
configuration:
Boot Layer
  add modules: java.base java.security.jgss jdk.security.auth jdk.security.jgss
  add exports: java.base/jdk.internal.misc ALL-UNNAMED
               java.base/sun.security.util ALL-UNNAMED
               java.security.jgss/sun.security.jgss ALL-UNNAMED
               java.security.jgss/sun.security.krb5 ALL-UNNAMED
               java.security.jgss/sun.security.krb5.internal ALL-UNNAMED
               java.security.jgss/sun.security.krb5.internal.ccache ALL-UNNAMED
               java.security.jgss/sun.security.krb5.internal.crypto ALL-UNNAMED
               java.security.jgss/sun.security.krb5.internal.ktab ALL-UNNAMED
               java.security.jgss/sun.security.krb5.internal.rcache ALL-UNNAMED
  add opens: java.security.jgss/sun.security.krb5 ALL-UNNAMED
               java.security.jgss/sun.security.krb5.internal ALL-UNNAMED

STDOUT:
Start KDC on 13371
Callback for name: dummy
Callback for pass: bogus
-----------------------------------------------
>>>>> UDP packet received
RABBIT.HOLE> dummy@RABBIT.HOLE sends AS-REQ for krbtgt/RABBIT.HOLE@RABBIT.HOLE, KDCOptions: FORWARDABLE,
KrbException: Additional pre-authentication required (25)
at KDC.processAsReq(KDC.java:1099)
at KDC.processMessage(KDC.java:646)
at KDC$1.run(KDC.java:1267)
     Error 25 Additional pre-authentication required
>>>>> UDP request honored
-----------------------------------------------
>>>>> UDP packet received
RABBIT.HOLE> dummy@RABBIT.HOLE sends AS-REQ for krbtgt/RABBIT.HOLE@RABBIT.HOLE, KDCOptions: FORWARDABLE,
     Return dummy@RABBIT.HOLE ticket for krbtgt/RABBIT.HOLE@RABBIT.HOLE, flags FORWARDABLE;INITIAL;PRE-AUTHENT
>>>>> UDP request honored
STDERR:
java.lang.NoClassDefFoundError: jdk/test/lib/JDKToolFinder
at jdk.test.lib.process.ProcessTools.createJavaProcessBuilder(ProcessTools.java:324)
at jdk.test.lib.process.ProcessTools.createJavaProcessBuilder(ProcessTools.java:311)
at ModuleName.main(ModuleName.java:49)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:563)
at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:115)
at java.base/java.lang.Thread.run(Thread.java:844)
Caused by: java.lang.ClassNotFoundException: jdk.test.lib.JDKToolFinder
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:553)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:185)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:486)
... 9 more

JavaTest Message: Test threw exception: java.lang.NoClassDefFoundError: jdk/test/lib/JDKToolFinder