At present three test classes:

test/hotspot/jtreg/vmTestbase/nsk/monitoring/stress/thread/strace001.java
test/hotspot/jtreg/vmTestbase/nsk/monitoring/share/ThreadController.java
test/hotspot/jtreg/vmTestbase/nsk/monitoring/share/thread/SleepingThread.java

examine the stack of a thread blocked in Thread.sleep. Every time the implementation of Thread.sleep changes (e.g. the JFR event, virtual threads) the list of expected stack frames needs to be updated. This is very tedious and we should find a way to avoid it.