I have the problem that when my table gets too wide so that I have to resize it, the thickness of \toprule and \bottomrule won't show any more. When I zoom in I can see that there still is a thickness variation between \midrule and the ones mentioned above. So I guess the thickness of \toprule and \bottomrule is resized, too? Does anyone have a solution how one can resize a table AND have bold lines in the table?
\begin{table}[th]
\caption[Test]{Test.} \label{tab:Test}
\centering
\resizebox{\textwidth}{!}{%
\begin{tabular}{lcccccccc}
\toprule
{} & {TestTestTestTest} & {TestTestTestTest} & {TestTestTestTest} & {TestTestTestTest} & {TestTestTestTest} & {TestTestTestTest} & {TestTestTestTest} & {TestTestTestTest} \\
\midrule
{TestTestTestTest} & \multirow{2}{*}{1000} & \multirow{2}{*}{1000} & \multirow{2}{*}{1000} & \multirow{2}{*}{1000} & \multirow{2}{*}{1000} & \multirow{2}{*}{1000} & \multirow{2}{*}{1000} & {} \\[-2mm]
{TestTestTestTest} & {} & {} & {} & {} & {} & {} & {} & {} \\
\bottomrule
\end{tabular}}
\end{table}

\resizeboxon tables at as a last resort and even then avoid doing it, there are always better ways. use a smaller font eg\smallor use column types likep{2cm}rather thancso the text in the cells can linebreak – David Carlisle Jan 29 '20 at 22:40\resizeboxto make the tabular material “fit” inside the width of the textblock is taking the sledgehammer approach. Why worry about the thickness of some horizontal lines if everything else in the table has experienced the equivalent of being smashed to pieces? – Mico Jan 29 '20 at 22:44