Back in the day, at the AM Broadcast transmitter site I worked at, we had just such a lead, except that it ended in bare conductors, not banana sockets.
It had a serious purpose, which was testing Mains "under-voltage" detectors, which were incorporated in the transmitters.
In the event of a "brown out", or other extended low supply voltage, the transmitters shut down to prevent damage to the high power air cooled tubes.
One of our regular "routines" was to disconnect the normal supply to these devices, which was connected via a screw type terminal strip, replacing it with the wires of the "suicide lead".
The other end of the lead was plugged into a Variac, the voltage was dropped, & we ascertained whether the detector worked correctly.
This lead was kept with the various other "useful cables" in a drawer in the workshop.
I was a bit paranoid, & if ever I saw it put away with the ends bare, I wrapped them in insulating tape, reasoning that if people had to unwrap the tape they would be reminded of the danger.
This was at a station with a small number of staff, all who were Technicians who worked on the "big bities" all the time, so the danger was really minimal.