This speedtest server is located at the Serverius datacenters, AS50673 and is running on a 10GE connection.

Serverius speedtest servers in DataCenter1 DAtaCenter2 DataCenter3

Test with IPERF

Iperf software and manuals you can find on official home page https://iperf.fr
You can find TCP Throughput calculator here.
For a more correct test, use the command like: 
iperf -c speedtest1.serverius.net -P 10    (for IPv4)
iperf -c speedtest1.serverius.net -V -P 10 (for IPv6)
Also you can use IPERFv3 (client sends, server receives) 
iperf3 -c speedtest1.serverius.net -p 5002 -P 10 -4    (for IPv4)
iperf3 -c speedtest1.serverius.net -p 5002 -P 10 -6    (for IPv6)
( -R reverse mode (server sends, client receives) 
iperf3 -c speedtest1.serverius.net -p 5002 -P 10 -4 -R  (for IPv4)
iperf3 -c speedtest1.serverius.net -p 5002 -P 10 -6 -R  (for IPv6)

Test with download files from HTTP

This archive is available over http on both IPv4 and IPv6.

10mb.bin, 100mb.bin, 1000mb.bin, 2000mb.bin, 5000mb.bin, 10000mb.bin
For a more correct test, use the command like: 
wget -4 -O /dev/null http://speedtest1.serverius.net/files/2000mb.bin (for IPv4)
wget -6 -O /dev/null http://speedtest1.serverius.net/files/2000mb.bin (for IPv6)
Serverius speedtest