Multirow column takes all the width in a table without setting colwidth

Here is a example (converted from a html table)
```
\begin{longtable}[]{@{}llll@{}}
\caption{test}\tabularnewline
\toprule\noalign{}
\endfirsthead
\endhead
\bottomrule\noalign{}
\endlastfoot
a & b & c & d \\
\multirow{2}{=}{test} & 1 & 2 & 3 \\
& 1 & 2 & 3 \\
\end{longtable}
```