\ifdefined\directlua
  \directlua{config = config or { luaotfload = { } }
             config.luaotfload.resolver = "cached"
             config.luaotfload.loglevel = 5 }
  \input luaotfload.sty
\fi

\font\iwona           =name:iwona      at 20pt
\font\iwonabold       =name:iwona/b    at 20pt
\font\iwonaitalic     =name:iwona/i    at 20pt
\font\iwonabolditalic =name:iwona/bi   at 20pt

\def\test{foo bar baz \endgraf}
{\iwona           \test}
{\iwonabold       \test}
{\iwonaitalic     \test}
{\iwonabolditalic \test}
\bye