The test never actually defined a function named 'alias1', not even
when zsh 5.4 warned it about this (see 9523d6d49cb3d4db5bd84c3cec6168a2057fe3ab,
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