There are several things that came to mind, when reading this question.
POSSIBILITY 1) \detokenize
David suggested this in a comment. The OP responded that he/she was unhappy with the space that \detokenize automatically introduces after macro names. That reminded me of this question, Print small TeX code verbatim and render it, which provided two answers. Egreg's accepted answer used an \ExplSyntaxOn approach (xparse package) in which
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand{\showcase}{v} { \texttt{#1} }
\ExplSyntaxOff
provides a verbatim macro. My timid attempt to incorporate this inside of another macro was unsuccessful, but I am unversed at \ExplsyntaxOn to know whether egreg's approach could be adapted for the needs of the OP.
The other answer at that question was my own, in which I introduced \detokenizeplus, to trap the annoying spaces and try to eliminate them. While I could make it work for that particular question, the approach was not bulletproof, as I noted in the answer. Nonetheless, there is the chance to employ \detokenizeplus within another macro to get the benefits of the \detokenize approach, but without the annoying spaces.
POSSIBILITY 2: verbatimbox
My verbatimbox package might also have so application here, though it is hard to tell, based on the limited example provided by the OP. What that package's verbbox environment does is to allow verbatim content to be saved inside a LaTeX box, to be later regurgitated with \theverbbox (note there is also a myverbbox environment that allows a unique name of the box to be specified).
So, while the verbatim content cannot be specified inside of a macro with this approach, previously specified verbatim content can be presented (inline) inside of the macro. Here is an example of how that is done:
\documentclass{article}
\usepackage{verbatimbox}
\newcommand{\FIXME}[1]{$>>>$#1$<<<$}
\begin{document}
\noindent
$>>>$\verb+test test test+$<<<$ \\
\FIXME{test test test}\\
\begin{verbbox}test test test\end{verbbox}
\FIXME{\theverbbox}\\
\end{document}

\verbin the argument to another command. But do you really need\verb? – egreg Oct 13 '15 at 21:26\texttt{#1}? – David Carlisle Oct 13 '15 at 21:35\texttt{\detokenize{#1}}probably does the right thing if you are using\usepackage[T1]{fontenc}– David Carlisle Oct 13 '15 at 21:46\FIXME{bla \text{AAA} bla}it gives an extra space\text<space>{AAA}which is not desirable. – cacamailg Oct 13 '15 at 21:51{}as the argument delimiter as{}are not special in verbatim, that is why for\verbthe user has to specify a characer that does not appar and use\verb^xxx^ orwhatever. – David Carlisle Oct 13 '15 at 22:29\detokenizeis discussed in this question/answers: http://tex.stackexchange.com/questions/128399/print-small-tex-code-verbatim-and-render-it. Now whether you can directly employ egreg's answer or use my\detokenizeplus, it remains to be seen. – Steven B. Segletes Oct 13 '15 at 23:37\usepackage{xparse} \ExplSyntaxOn \NewDocumentCommand{\showcase}{v} { \texttt{#1} } \ExplSyntaxOff– Steven B. Segletes Oct 13 '15 at 23:44verbatimboxpackage may be useful. Theverbboxenvironment savesverbatimcontent into a LaTeX box, which can be recalled, either on the command line, or inside a macro with\theverbbox. – Steven B. Segletes Oct 13 '15 at 23:50verbatimboxexample. Let me know if it is relevant.\documentclass{article} \usepackage{verbatimbox} \newcommand{\FIXME}[1]{$>>>$#1$<<<$} \begin{document} \noindent $>>>$\verb+test test test+$<<<$ \\ \FIXME{test test test}\\ \begin{verbbox}test test test\end{verbbox} \FIXME{\theverbbox}\\ \end{document}– Steven B. Segletes Oct 13 '15 at 23:58