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

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

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+\documentclass{article}
+\usepackage{mathtools}
+
+\begin{document}
+
+\begin{align}
+  f(x) &= \bigg\lvert 0 \bigg\rvert \\
+  f(x) &= \Bigg\lVert 0 \Bigg\rVert \\
+\end{align}
+
+\[
+  \begin{multlined}[b]
+    \framebox[4cm]{first} \\
+    \framebox[4cm]{last}
+  \end{multlined} = B
+  \begin{multlined}[b][7cm]
+    \framebox[4cm]{first} \\
+    \framebox[4cm]{last}
+  \end{multlined} = B
+\]
+
+\begin{align*}
+  f(a) &=
+  \!\begin{aligned}[t]
+    & \frac{1}{2}+\cdots \\& \dots+\frac{1}{2}
+  \end{aligned}
+\end{align*}
+
+\begin{equation}
+  \begin{lgathered}[c]
+    x=1,\quad x+1=2 \\
+    y=235
+  \end{lgathered}
+\end{equation}
+
+\[
+  \begin{pmatrix*}[r]
+    -1 & 3 \\
+    2  & -4
+  \end{pmatrix*}
+\]
+
+\[
+  \begin{smallmatrix*}[r]
+    -1 & 3 \\
+    2  & -4
+  \end{smallmatrix*}
+\]
+
+\begin{gather}
+  f(x) = x
+  \shortintertext{This is a short intertext.}
+  f(x) = x
+\end{gather}
+
+\end{document}