How to divide circle multipart nodes in tikz [duplicate]

I would like to get multi part node with vertical line between lower nodepart. Something like this:

My code:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{arrows}
\usetikzlibrary{shapes.multipart}
\begin{document}
\begin{tikzpicture}[->,>=stealth',shorten >=1pt,auto,node distance=3cm,
thick,main node/.style={circle,fill=blue!20,draw,font=\sffamily\Large\bfseries}]
\node [circle split,draw,double,fill=red!20]
{
$q_1$
\nodepart{lower}
{
test1
}
{
test2
}
};
\end{tikzpicture}
\end{document}


What should i add to this to get vertical line between test1 and test2?