Misalignment in a siunitx column with asterisks and different integer parts

Question

In the following MWE the last number in the test statistic column, doesn't get aligned to the decimal separator. Although the additional asterisks are explicitly defined in the column definition. I tried a lot of different options, but could not get it to work properly.

\documentclass{article}
\usepackage{breqn}
\usepackage{siunitx}
\usepackage{tabularx}
\usepackage{booktabs}
\begin{document}
\begin{table}[htb]
  \newcommand{\ColWidthTestResults}{0.12}
   \footnotesize
    \sisetup{table-parse-only}
 \begin{center} 
\begin{tabularx}{\textwidth}{>{\centering}X
                                >{\centering}p{0.005\textwidth}
                                 S[table-format=3.2
                                  , table-number-alignment = center 
                                  , table-space-text-post = {$^{***}$} 
                                  , table-space-text-pre = {$^{***}$} 
                                  , round-precision=2
                                  , round-integer-to-decimal = true
                                  ]
                                 >{\centering}p{0.005\textwidth}
                                 >{\centering}p{\ColWidthTestResults\textwidth}
                                 >{\centering}p{\ColWidthTestResults\textwidth}
                                 >{\centering}p{\ColWidthTestResults\textwidth}
                                  }
        \toprule
rank       & & {test statistic} & & 10\% &  5\%  & 1\% \tabularnewline
\cmidrule{1-1}      \cmidrule{3-3}  \cmidrule{5 - 7}       
r $\leq$ 2 & &   \num{2.88} & & 21.03 & 23.60 & 28.94\tabularnewline
r $\leq$ 1 & &  \num{23.58}     & & 42.20  & 45.54 &  52.27\tabularnewline
r $=$    0 & & \num{236.20}{$^{***}$}  & & 67.02 & 71.08  & 79.11 \tabularnewline
\bottomrule
\end{tabularx}\caption{Misaligned decimal separator}
\end{center}
\end{table} 
\end{document} 

Ideally the numbers should all be aligned on the decimal separator, no matter how many asterisks or how long the integer part of the decimals is.

Answer 1

This code works fine for me. The culprit is \sisetup{table-parse-only}. I took the opportunity to make a few corrections to your code. In particular don't use a center environment inside table: it adds unwanted vertical spacings. Use \centering instead.

\documentclass{article}
\usepackage{breqn}
\usepackage{siunitx}
\usepackage{tabularx}
\usepackage{booktabs}

\begin{document}

\begin{table}[!htb]
  \newcommand{\ColWidthTestResults}{0.12}
   \footnotesize
 \centering
\begin{tabularx}{\textwidth}{>{\centering $}X<{$}S[table-format=3.2
                                  , table-number-alignment = center
                                  , table-space-text-post = {$^{***}$}
                                  , table-space-text-pre = {$^{***}$}
                                  , round-precision=2
                                 , round-integer-to-decimal = true
                                  ]
                                 >{\centering}p{\ColWidthTestResults\textwidth}
                                 >{\centering}p{\ColWidthTestResults\textwidth}
                                 >{\centering}p{\ColWidthTestResults\textwidth}
                                  }
        \toprule
\mathrm{rank} & {test statistic} & 10\,\% & 5\,\% & 1\,\% \tabularnewline%
\cmidrule(lr){1-1} \cmidrule(lr){2-2} \cmidrule(lr){3-5}
r \leq 2 & 2.88 & 21.03 & 23.60 & 28.94\tabularnewline
r \leq 1 & 23.58 & 42.20 & 45.54 & 52.27\tabularnewline
r = 0 & 236.20 {$^{***}$} & 67.02 & 71.08 & 79.11 \tabularnewline
\bottomrule
\end{tabularx}
\caption{Misaligned decimal separator}
\end{table}

\end{document} 

Answer 2

To be honest, I do not quite understand why you are using the \num{} command in an S-column. Maybe I did not get what you are trying to do.

Do you want to achieve the following? Rounded values with alignment and some asterisks?

% arara: pdflatex

\documentclass{article}
\usepackage{siunitx}
\usepackage{tabularx}
\usepackage{booktabs}

\begin{document}
    \begin{table}[htb]
        \newcommand{\ColWidthTestResults}{0.12}
        \footnotesize
            \begin{tabularx}{\textwidth}{>{\centering}X
                    S[table-format=3.2
                    ,table-space-text-post = {***} 
                    ,round-mode=places
                    ,round-precision=2
                    ,table-align-text-post = false
                    ]
                    >{\centering}p{\ColWidthTestResults\textwidth}
                    >{\centering}p{\ColWidthTestResults\textwidth}
                    >{\centering}p{\ColWidthTestResults\textwidth}
                }
                \toprule
                rank       & {test statistic} &  10\,\% &  5\,\%  & \SI{1}{\percent} \tabularnewline
                \cmidrule(r){1-1}      \cmidrule{2-2}  \cmidrule(l){3 - 5}       
                r $\leq$ 2 &   2.88 &  21.03 & 23.60 & 28.94\tabularnewline
                r $\leq$ 1 &  23.58     &  42.20  & 45.54 &  52.27\tabularnewline
                r $=$    0 & 236.20111111*** &  67.02 & 71.08  & 79.11 \tabularnewline
                \bottomrule
            \end{tabularx}\caption{Perfectly aligned decimal separator}
    \end{table} 
\end{document} 

I would advice you not to do the tabularx stuff and the font size tweaking, but I do not know, what your whole table looks like. For sure, I would tend to set the last three columns as S-columns as well. Or at least set the numbers in \num or $ $ commands.

Here is what it looks like so far: