%%
%% The LaTeX Companion, 3ed
%%
%% Example 16-7-34 on page II-564 in "Core configuration files and commands".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{147.0pt}
%
% Use biber program
\setlength\parindent{0pt}
\usepackage{biblatex}
\addbibresource{tlc-ex.bib}

%StartShownPreambleCommands

%StopShownPreambleCommands

\begin{document}
\DeclareCiteCommand{\citetesting}[\textit]
  {BEFORE }{\textbf{\thefield{entrykey}}}{ SEP }{ AFTER}
\citetesting{article1,article2,article3}
\end{document}