$ CONF=linux-x86_64-server-fastdebug make test TEST=sun/tools/jhsdb/heapconfig/JMapHeapConfigTest.java TEST_VM_OPTS="-XX:+UseShenandoahGC"

STDERR:
java.lang.RuntimeException: Key 'G1HeapRegionSize' doesn't exists in jmap output
        at JMapHeapConfigTest.compareValues(JMapHeapConfigTest.java:104)
        at JMapHeapConfigTest.main(JMapHeapConfigTest.java:161)
        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)

This happens because Shenandoah path does not print G1HeapRegionSize at all:
 https://github.com/openjdk/jdk/blob/ed585d16b9069a678bb8633239ca87f64c956fdd/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/tools/HeapSummary.java#L89-L93