\input luaotfload.sty

\font\testa={Latin Modern Roman/S=12} at 10pt
\font\testb={Latin Modern Roman}      at 5pt
\font\testc={Latin Modern Roman}      at 10pt
\font\testd={Latin Modern Roman/S=15} at 10pt
\font\teste={Latin Modern Roman/S=3}  at 10pt
\testa abcd ABCD \par
\testb abcd ABCD \par
\testc abcd ABCD \par
\testd abcd ABCD \par
\teste abcd ABCD \par
\bye
