I have the following abstracted code. I do not know why the text test
is not centered. Do you know how to make it centered?
\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning, math, fit, backgrounds}
\begin{document}
\begin{tikzpicture}
\node [draw = black] {A TEST};
\coordinate (a) at (current bounding box.south east); \draw (a) circle (3pt);
\coordinate (b) at ([yshift = -15 pt]current bounding box.south west);
\node (MEM) [inner sep = 0, fit = (a) (b), fill=black!20!red] {test};
\end{tikzpicture}
\end{document}
Result: