Factor out common strings in tests

3 jobs for customize-ui in 2 minutes and 26 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build Pkgsrc
passed build_pkgsrc:stretch #15346

00:00:11

 
  Build Pkg
passed build_pkg:stretch:amd64 #15347
amd64

00:00:30

passed build_pkg:stretch:arm64 #15348
arm64

00:02:14