The test was recently added, but was then failing due to JDK-8155092 "[TESTBUG] TestHumongousClassLoader.java needs UnlockDiagnosticVMOptions before WhiteBoxAPI ".

8155092 is fixed, and now the test seems to be failing as intended:

----------System.err:(16/1350)----------
java.lang.RuntimeException: Classloader class HumongousClassLoader is loaded after we forget all references to it (assert failed: true == false)
at jdk.test.lib.Asserts.error(Asserts.java:447)
at jdk.test.lib.Asserts.assertTrue(Asserts.java:374)
at jdk.test.lib.Asserts.assertEquals(Asserts.java:169)
at gc.g1.humongousObjects.TestHumongousClassLoader.main(TestHumongousClassLoader.java:209)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(java.base@9-internal/Native Method)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(java.base@9-internal/NativeMethodAccessorImpl.java:62)
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(java.base@9-internal/DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(java.base@9-internal/Method.java:531)
at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:110)
at java.lang.Thread.run(java.base@9-internal/Thread.java:843)

JavaTest Message: Test threw exception: java.lang.RuntimeException: Classloader class HumongousClassLoader is loaded after we forget all references to it (assert failed: true == false)
JavaTest Message: shutting down test

STATUS:Failed.`main' threw exception: java.lang.RuntimeException: Classloader class HumongousClassLoader is loaded after we forget all references to it (assert failed: true == false)

As this is a new test, it could be a bug in GC or a bug in the test.