Add (failing) test coverage for !23

This demonstrates the behaviour we want from !23.

Signed-off-by: Simon McVittie <smcv@collabora.com>
3 jobs for test-library-choice in 36 minutes and 33 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Test
passed build:bionic #15984

00:16:54

passed build:buster #15983

00:20:54

passed build:stretch #15982

00:23:19