%% test-ptex.tex
%% =============
%% Typesetting test for (u)pLaTeX: a long footnote near the page bottom
%% is moved to the next page as a whole.
%%
%%   uplatex test-ptex.tex && dvipdfmx test-ptex
%%   platex  test-ptex.tex && dvipdfmx test-ptex
%% The class is selected automatically (platex: jbook / uplatex: ujbook).
%% Since current pLaTeX also runs on the e-upTeX engine, the format is
%% detected via the internal kanji encoding.
%%
%% The number of filler lines is set by \FILLN (default 68, which
%% triggers the phenomenon on TeX Live 2026; scan nearby values if the
%% layout changes with your TeX distribution):
%%   uplatex -jobname=test-ptex-n70 "\def\FILLN{70}\input test-ptex.tex"
%% For a control build without the package (only
%% \interfootnotelinepenalty=10000):
%%   uplatex -jobname=test-ptex-off "\def\NOPKG{1}\input test-ptex.tex"
%%
%% What to check:
%%   * The ordinary footnote (page 1) is typeset as usual.
%%   * At the trigger boundary the long footnote moves to the next page;
%%     in the control build the original page ends with a lone
%%     \footnoterule (no footnote text below it), while with the package
%%     the lone rule disappears.
%%
%% The phenomenon requires \raggedbottom (or bottom glue with stretch)
%% and an \@makefntext that starts with vertical material (a leading
%% \kern), as in many book-production classes.
\ifnum\jis"2121="3000
  \documentclass{ujbook}
\else
  \documentclass{jbook}
\fi
\ifdefined\NOPKG
  \interfootnotelinepenalty=10000
\else
  \usepackage{footnotenosplit}
  \footnotetopkern=2pt
\fi
\raggedbottom
\makeatletter
\renewcommand\@makefntext[1]{%
  \kern 2\p@
  \parindent 1em\noindent
  \hb@xt@1.8em{\hss\@makefnmark}#1}
\makeatother
\ifdefined\FILLN\else\def\FILLN{68}\fi
\begin{document}
\chapter{Test}
Start of the test\footnote{An ordinary footnote that fits on the same page.}.
\newcount\mycount \mycount=0
\loop
  \advance\mycount by 1
  This is a filler line of plain English text to fill the page.\par
\ifnum\mycount<\FILLN \repeat
REFLINE is the reference line at the very bottom of this page\footnote{LONGNOTE: this footnote is quite long, so it cannot fit on the current page and should move to the next page as a whole. This footnote is quite long, so it cannot fit on the current page and should move to the next page as a whole.}.

Text on the next page.
\end{document}