dotfiles/dot_vim/plugged/vimtex/test/test-completion-bibtex/test_custom_bibs.tex

\documentclass{amsart}
\newcommand{mybibliography}[1]{
  \phantomsection\addcontentsline{toc}{subsubsection}{Reference}
  \bibliography{#1}
}

\mybibliography{test_custom_bibs}

\begin{document}
Test
\end{document}