TopCoder Arena – TZTester doesn’t work

If you compete in the TopCoder SRMs, the TZTester plugin is very useful. It calls all the tests for you and displays the results, saving valuable minutes in the arena.
I used it with my old computer but couldn’t get it working on my new one, and with the clock counting down, sod’s law was against me.
$RUNTEST$ and $TESTCODE$ sat in my template, stubbornly refusing to become useful C++ code.
The solution was simple – I found it here.
Just make CodeProcessor your default editor, instead of (in my case) popsEdit.