I had the same problem with Centos 7 and Oracle JDK 8. Those exact unit tests would fail. Follow the instructions on https://nifi.apache.org/quickstart.html. I think you'll find that Centos sets max file handles to 1024 for a user.
I also had to increase net.core.rmem_max to 1,200,000 to pass one of the Syslog tests. George George
