I have to define a new environment doing something like that.
\documentclass[12pt]{article}
\usepackage{tcolorbox,empheq}
\begin{document}
\begin{tcolorbox}
\begin{empheq}{align}
a=b
\end{empheq}
\end{tcolorbox}
\end{document}
This code works fine, but if I try something like testa or testb, I get errors.
\documentclass[12pt]{article}
\usepackage{tcolorbox,empheq}
\newenvironment{testa}{\tcolorbox\empheq{align}}{\endempheq\endtcolorbox}
\newenvironment{testb}{\tcolorbox\setkeys{EmphEqEnv}{align}\EmphEqMainEnv}{\endEmphEqMainEnv\endtcolorbox}
\begin{document}
\begin{testa}
a=b
\end{testa}
\end{document}
Is there a solution ?