%% non-standard fonts deserve an extra test file
\documentclass{scrartcl}
\usepackage{fontspec}
%% ····································································
%% libertine monospace
%% -------------------
%% real-world example from: http://tex.stackexchange.com/q/110566
%% causing database lookups to fail; addressed in luaotfload since
%% https://github.com/phi-gamma/luaotfload/commit/4d0d2c19ab36d4918a72041a087fbcb451ac8c52
\setmonofont{Linux Libertine Mono O}
%% ····································································

\begin{document}
  foo {\ttfamily bar} baz
\end{document}