\documentclass[a4paper]{article}

\usepackage{pgfplots}

\usetikzlibrary{external}
\tikzexternalize[mode=list and make]

\begin{document}
\begin{tikzpicture}
	\begin{axis}
	\addplot table {unittest_external_make.dat};
	\end{axis}
\end{tikzpicture}
\end{document}

