vimtex/test/feature/completions/main.tex

\documentclass{article}
\usepackage{biblatex}
\addbibresource{biblatex-examples.bib}
\addbibresource{local1.bib}
\addbibresource{~/.vim/bundle/vim-latex/test/completion/local2.bib}
\begin{document}

To test label completion you need to compile the document first!

\begin{equation}
  f(x) = 42
  \label{eq:main-is-working}
\end{equation}

\include{sub1}

\include{"sub2\space with\space spaces"}

\input{"sub3\space with\space spaces"}

\end{document}