R Under development (unstable) (2025-02-18 r87748 ucrt) -- "Unsuffered Consequences"
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> 
> library(xdvir)
            TeX:  C:\PROGRA~1\MiKTeX\miktex\bin\x64\latex.exe
          xetex:  MiKTeX-XeTeX 4.9 (MiKTeX 23.1)
         luatex:  This is LuaTeX, Version 1.16.0 (MiKTeX 23.1)
luaotfload-tool:  3.23
> 
> author("This is a test: $x - \\mu$")
%% R package xdvir_0.1.0; engine name: LuaTeX; engine version: This is LuaTeX, Version 1.16.0 (MiKTeX 23.1); packages: 
\documentclass[varwidth]{standalone}
\usepackage{unicode-math}
\begin{document}
This is a test: $x - \mu$
\end{document}
> 
> ## Invalid engine
> tools::assertError(author("test", engine=NULL))
> 
> ## Explicit engine
> author("test", engine=xdvir:::nullEngine)
%% R package xdvir_0.1.0; engine name: null; engine version: 0.1.0; packages: 
\documentclass[varwidth]{standalone}

\begin{document}
test
\end{document}
> 
> ## Engine by name
> author("test", engine="null")
%% R package xdvir_0.1.0; engine name: null; engine version: 0.1.0; packages: 
\documentclass[varwidth]{standalone}

\begin{document}
test
\end{document}
> 
> ## Unknown engine (name)
> tools::assertError(author("test", engine="unknown"))
> 
> proc.time()
   user  system elapsed 
   0.21    0.15    3.96