$ CONF=linux-x86_64-server-fastdebug make test TEST=gc/stringdedup TEST_VM_OPTS="-XX:+UseShenandoahGC -XX:+ShenandoahVerify"

# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/home/shade/trunks/jdk/src/hotspot/share/gc/shenandoah/shenandoahVerifier.cpp:923), pid=664457, tid=664504
# guarantee(cl_size == heap_used) failed: Generic Verification: heap used size must be consistent: heap-used = 94482K, regions-used = 85522K

Might be a simple accounting error somewhere.