当宏/命令使用可选参数定义时，无法显示宏/命令定义

Question

例如，我定义了两个命令。\mytesta带有可选参数，\mytestb不带有可选参数。现在使用\cs_meaning:N显示命令定义。结果如下：

\documentclass{article}
\newcommand{\mytesta}[2][]{#2\quad#1}
\newcommand{\mytestb}[2]{#1\quad#2}
\setlength{\parindent}{0pt}
\ExplSyntaxOn
\cs_set_eq:NN \checkmeaning \cs_meaning:N
\ExplSyntaxOff

\begin{document}
\Large
\section{Testing}
\par\mytesta[default]{argument}
\par\mytestb{argument}{default}

\vskip 2em
\par\verb|\mytesta:|
{\par\ttfamily\checkmeaning \mytesta}
\par\verb|\mytestb:|
{\par\ttfamily\checkmeaning \mytestb}

\vskip 2em
\par\verb|Is possible to show:|
\par\verb|"[#1]#2->#2\quad #1" in \mytesta?|
\end{document}