test/langtools/jdk/javadoc/doclet/testIOException/TestIOException.java fails when run with root user

test log snippet:
STDOUT:
Running test testReadOnlyFile
STDERR:
java.lang.reflect.InvocationTargetException
        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:566)
        at javadoc.tester.JavadocTester.runTests(JavadocTester.java:274)
        at javadoc.tester.JavadocTester.runTests(JavadocTester.java:258)
        at TestIOException.main(TestIOException.java:43)
        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:566)
        at com.sun.javatest.regtest.agent.MainWrapper$MainTask.run(MainWrapper.java:138)
        at java.base/java.lang.Thread.run(Thread.java:955)
Caused by: java.lang.Error: index is writable
        at TestIOException.testReadOnlyFile(TestIOException.java:82)
        ... 13 more