The test never actually defined a function named 'alias1', not even
when zsh 5.4 warned it about this (see 9523d6d49c,
which was wrong and is hereby reverted).
The test that's now failing has been filed as issue #558.
All these files should be sourced, not executed; and Debian's lintian complains:
W: zsh-syntax-highlighting: script-not-executable usr/share/zsh-syntax-highlighting/zsh-syntax-highlighting.zsh