There is an update below for current version of UniFi OS
In the old days the cable test was available through the CLI:
swctrl -d cable show
And you should expect something similar like:
BusyBox v1.19.4 (2017-03-10 11:34:48 PST) built-in shell (ash)
Enter 'help' for a list of built-in commands.
US.v3.7.47# swctrl -d cable show
Port Status Distance
---- --------------- ---------------
1 Normal 7m - 32m
2 No Cable
3 Normal 0m - 185m
4 Normal 0m - 15m
5 No Cable
6 Normal 0m - 10m
7 No Cable
8 No Cable
US.v3.7.47#
But if you try to use this command these days you will get the info message:
This command is deprecated, please use command 'swctrl port' instead.