You could just kill the offending test script process using the task manager or some other similar tool

Yes, my original post was built around a false assumption - namely, that Ctrl-C was the only way I could escape from the hang.
As salva suggested, procexp, makes it quite easy to select and kill the appropriate process.
One can even double check that one has selected the correct perl process (prior to killing that process) by looking at its command line, which is displayed under its "Properties".

Thank you, salva.
Thanks also to 1nickt for a handy idea. (1nickt's idea was more in line with what I initially expected was going to be needed.)

Cheers,
Rob