
\documentclass{testsuite}
\usepackage{fontspec}
\begin{document}
\ExplSyntaxOn
LM~is
\fontspec_if_fontspec_font:TF {\ERROR}{~not~a~fontspec~font.\par}

\setmainfont{TeX~ Gyre~ Pagella}
TeX Gyre Pagella
\fontspec_if_fontspec_font:TF {~is~a~fontspec~font}{\ERROR}

\fontspec_if_opentype:TF {,~is~OpenType}{\ERROR}

\fontspec_if_feature:nTF {smcp}{,~has~small~caps}{\ERROR}

\fontspec_if_current_script:nTF {latn}{,~is~using~Latin~script}{\ERROR}

\fontspec_if_script:nTF {cyrl}{,~also~has~Cyrillic}{\ERROR}

\fontspec_if_current_language:nTF {DFLT}{,~is~using~`default'~language}{\ERROR}

\fontspec_if_language:nnTF {latn}{ROM}{,~also~has~Romanian}{\ERROR}

\end{document}