TikZ's extended line penetrates the figure caption

Question

Here is an example:

\documentclass{article}
\usepackage{tikz}

\begin{document}

\begin{figure}\centering

\begin{tikzpicture}[extended line/.style={shorten >=-#1,shorten <=-#1}]
\draw [very thick, extended line=1cm] (0,0) -- (0,1);
\end{tikzpicture}

\caption{This is a test caption.}
\end{figure}

\end{document}

and its outcome:

How can I move the tikzpicture above the caption?

Answer 1

Is this a valid option?

Code

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\tikzset{
    extended line/.style={
        to path={
            ($(\tikztostart)!-#1!(\tikztotarget)$) --  ($(\tikztotarget)!-#1!(\tikztostart)$) \tikztonodes
        }
    }
}
\begin{document}
\begin{figure}\centering
\begin{tikzpicture}
\draw [very thick] (0,0) to[extended line=1cm] (0,1);
\end{tikzpicture}
\caption{This is a test caption.}
\end{figure}
\end{document}