my-resolver.lvt

% !Mode:: "TeX:DE:UTF-8:Main"
\input{regression-test}
\documentclass{article}
\usepackage{luacode}

\begin{document}
\START
\showoutput

\begin{luacode}
  local my_fonts = {
    rm = kpse.find_file("lmroman10-regular.otf", "opentype fonts"),
    sf = kpse.find_file("lmsans10-regular.otf", "opentype fonts"),
    dh = kpse.find_file("lmromandunh10-regular.otf", "opentype fonts"),
  }
  luatexbase.add_to_callback("luaotfload.resolve_font", function(spec)
    return my_fonts[spec.name]
  end, "luaotfload.test_resolver")
\end{luacode}
\font\myrm my:rm at 10pt
\font\mysf my:sf at 10pt
\font\mydh my:dh at 10pt
\myrf Some \mysf nice \mydh fonts!
\end{document}