variable font test

\documentclass{article}
\usepackage{fontspec}
\setmainfont{SourceSerif4Variable-Roman.otf}
\begin{document}
\addfontfeatures{RawFeature={+axis={wght=100}}}
The quick brown fox jumps over the lazy dog. \par
\addfontfeatures{RawFeature={+axis={wght=300}}}
The quick brown fox jumps over the lazy dog.\par
\addfontfeatures{RawFeature={+axis={wght=300,opsz=10}}}
The quick brown fox jumps over the lazy dog.\par
\addfontfeatures{RawFeature={+axis={wght=300,opsz=24}}}
The quick brown fox jumps over the lazy dog.\par
\addfontfeatures{RawFeature={+axis={wght=600}}}
The quick brown fox jumps over the lazy dog.\par
\addfontfeatures{RawFeature={+axis={wght=900}}}
The quick brown fox jumps over the lazy dog.
\end{document}