Dave Liquorice wrote:

I should hope it places a resistor between L and N and across the
current transformer. So that it actually tests what it is supposed to
be doing rather than relying on another path that might not exist.

But a resistor between L & N only simulates a load so it won't trip the RCD.
A RCD relies on an imbalance between the current in the Live wire and the
current in the Neutral wire. So the test will put a resistor between L and
Earth or between N and Earth. If you put a resistor between L & N the same
current flows in both wires so won't trip the breaker.

Trust me I work with electricity every day.

--
Malc
R1100RS old and tatty

You laugh at me because I am different
I laugh at you because you are all the same