The test is very finicky with the heap size. Consider adapting it so that it also works with Generational ZGC.

make test TEST=com/sun/jdi/ThreadMemoryLeakTest.java TEST_VM_OPTS="-XX:+UseZGC -XX:+ZGenerational"

Progress: 54000
Progress: 55000
Progress: 56000
Progress: 57000
Progress: 58000
Timeout signalled after 480 seconds
STDERR:
[2ms] run argError: Some tests failed or other problems occurred.
s: [ThreadMemoryLeakTarg]
[5824ms] Got ThreadStartEvent #1000 threads:157
Exception in thread "JDI Target VM Interface" java.lang.OutOfMemoryError: Java heap space
at java.base/java.net.Socket$SocketInputStream.read(Socket.java:1092)
at jdk.jdi/com.sun.tools.jdi.SocketConnection.readPacket(SocketConnection.java:83)
at jdk.jdi/com.sun.tools.jdi.TargetVM.run(TargetVM.java:123)
at java.base/java.lang.Thread.runWith(Thread.java:1583)
at java.base/java.lang.Thread.run(Thread.java:1570)

The heap is restricted to 7m so if there is a leak it can be quickly detected. However in this case it has run very few iterations, and then times out because "JDI Target VM Interface" got an OOME, preventing the test from making further progress. I tried 8m and that had the exact same result, so there is probably already rounding being done up to 8m. I then tried 9m and it passed.