To perform heavy duty tests you need to tune your OS.
MacOS X / macOS
The OS-settings for the maximum number of network connections per process is restricted by default to a value of 256 on almost all MacOS X versions. You can verify this value by entering the command "ulimit -n" from a terminal. This default value is too small to execute even small tests from MacOS X systems and it is also too small to monitor remotely executed cluster jobs executed on any other machines.
We recommend that you tune your MacOS X / macOS system.
To review the default (non-tuned) settings:
Enter "ulimit -n". Typically you will see: 256
Enter "launchctl limit". Typically you will see: maxproc 709 1064
maxfiles 256 unlimited
Tuning instructions:
Open a Finder window and navigate to the installation subdirectory /MacTuning(typically at /applications/zerbratester/mactuning)
Click on DoMacTuning.command
A terminal window appears. Enter first <return> to continue and then enter the superuser password (sudo root password)
Restart the MacOS X / macOS system (reboot).
Verify the new settings after the restart. Open a terminal window and enter "ulimit -n" and "launchctl limit"