What test case does : 
set Idle time 30 sec for a 100 entry map
wait 25 sec and touch 20 entries in the map
launch two Hz Instance and trigger migration
assert that map.size = 20 (80 is evicted already)

I have found 30 sec. is min. for second batch(20 entries) not to evicted becuase of Hz instance launches.

I just refactored test case but if you have any other suggestion, we can change the structure of test case.