I broke up with neovim....vim is my best friend now

dot_vim/plugged/vimtex/test/test-syntax/test-cases.tex

@@ -0,0 +1,16 @@
+\documentclass{article}
+\usepackage{cases}
+
+\begin{document}
+
+\begin{numcases}{y_1 = }
+  f_1(x) & $x > 0$\\
+  f_2(x) & $x \leqslant 0$
+\end{numcases}
+
+\begin{subnumcases}{y_1 = }
+  f_1(x) & $x > 0$\\
+  f_2(x) & $x \leqslant 0$
+\end{subnumcases}
+
+\end{document}