I was investigating my WiFi access points for improvement and while browsing the web for ideas I came across iperf3. Simple and effective, iperf3 is a tool to measure network bandwidth (read more about it ...)
To simplify installation, I created a MacOS X (Intel) installer package for iperf3 so you do not need to compile yourself.
(download iperf3.pkg)
An Universal Binary Installer Package for MacOS X can be found on NCSA Illinois, although that is iperf2.
(download iperf.pkg)

Simple 1-2-3 Network test:
Install iperf3 on a Mac where you start it as a server: open Terminal and enter the following:
iperf3 -s
Then install it on another Mac and run it as a client: open Terminal and enter:
iperf3 -c 192.168.178.131 -t 60 -P 2
where you must replace this IP-address with yours where iperf3 runs as a server on.

Wait a minute (-t 60) and the results are presented as follows:
Connecting to host 192.168.178.131, port 5201
[ 4] local 192.168.178.13 port 65334 connected to 192.168.178.131 port 5201
[ 5] local 192.168.178.13 port 65335 connected to 192.168.178.131 port 5201
[ ID] Interval Transfer Bandwidth
Sent
[ 4] 0.00-60.00 sec 342 MBytes 47.8 Mbits/sec
Received
[ 4] 0.00-60.00 sec 342 MBytes 47.8 Mbits/sec
Sent
[ 5] 0.00-60.00 sec 321 MBytes 44.9 Mbits/sec
Received
[ 5] 0.00-60.00 sec 321 MBytes 44.9 Mbits/sec
Total sent
[SUM] 0.00-60.00 sec 663 MBytes 92.7 Mbits/sec
Total received
[SUM] 0.00-60.00 sec 663 MBytes 92.7 Mbits/sec

iperf Done.

To stop the server, press CTRL-C.
Enter iperf3 --help  for all possible options.

This suite is also available on iOS: WiFi Bench.