Flavio, I think you should add
if (leadThread != null)
at the end of your new test. I have the succeeding test periodically failing because the 33556 port used by both tests for the leader quorum port is still in use. Adding the code above would wait until the leader shuts down in your test.
Actually, in addition to the above fix, I think we should change all the manually assigned ports in Zab1_0Test to be assigned using Portassignment.unique() like in other tests (I can do that if people agree that this should be done). If I understand correctly the static counter used in unique() to assign ports is initialized once per test file, so it would also prevent the problem I'm seeing here of two tests in the same file trying to use the same port.
Unfortunately I'm only seeing this in my branch and not in trunk.