As suggested in emacs-devel@ [1], this patch adds ert-lont-lock.el to
Emacs. Ert-font-lock is an extension to ERT providing an easy way to
check font faces either in inline strings or resource files.

The assertion syntax is based on Tree-sitter's syntax highlighter unit
tests [2]. This makes it easy to port existing tree-sitter grammar
tests to support both new-style ts-based major modes and the
traditional ones.

[1] https://lists.gnu.org/archive/html/emacs-devel/2023-11/msg00867.html
[2] https://tree-sitter.github.io/tree-sitter/syntax-highlighting#unit-testing
-- 
Regards,

Vladimir Kazanov