%% test-mag.tex
%% ============
%% \mag other than 1000 is not supported: the package warns and draws
%% nothing.
%%
%%   platex test-mag.tex && dvipdfmx test-mag
%%   lualatex test-mag.tex
%%
%% What to check:
%%   * the log has "Package showhanmengrid Warning: \mag=1200 is not
%%     supported".
%%   * SHG-MAG OK: the grid was not set up (nothing is drawn).
\ifdefined\directlua
  \documentclass{ltjarticle}
\else
  \documentclass{jarticle}
\fi
\mag=1200
\usepackage{showhanmengrid}
\makeatletter
\AddToHook{begindocument/end}[test]{%
  \ifdim\shg@zw=\z@\typeout{SHG-MAG OK}\else\typeout{SHG-MAG NG: the grid was set up}\fi}
\DeclareHookRule{begindocument/end}{showhanmengrid}{before}{test}
\makeatother
\begin{document}
本文です。
\end{document}