jdk.test.lib.classloader.ClassUnloadCommon$TestFailure: Test failed: should have been unloaded
at jdk.test.lib.classloader.ClassUnloadCommon.failIf(ClassUnloadCommon.java:51)
at UnloadTest.test_unload_obj_array_klass(UnloadTest.java:113)
at UnloadTest.main(UnloadTest.java:55)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
at com.sun.javatest.regtest.agent.MainWrapper$MainTask.run(MainWrapper.java:138)
at java.base/java.lang.Thread.run(Thread.java:1570)

The cause is explained in JDK-8310218. This issue exists for an targeted change to try and make the JDK tests pass.