\documentclass[varwidth=true, border=2pt]{standalone}
\usepackage{tikz}
\usepackage{pgfplots}
\usepackage{amsmath,amssymb}

\begin{document}
\begin{tikzpicture}
    \begin{axis}[
        axis x line=middle,
        axis y line=middle,
        xmin=-1.5,     % start the diagram at this x-coordinate
        xmax= 1.5,    % end   the diagram at this x-coordinate
        ymin=-1.5,     % start the diagram at this y-coordinate
        ymax= 1.5,   % end   the diagram at this y-coordinate
        ticks=none,
        enlargelimits=true,
        after end axis/.code={
            \draw [decorate,decoration={brace,mirror,raise=2pt}] (axis cs:0,1) -- (axis cs:-1,1) node [midway,above=5pt] {$r$};
            \draw [decorate,decoration={brace,mirror,raise=2pt}] (axis cs:1,1) -- (axis cs:0,1) node [midway,above=5pt] {$r$};
            \draw [decorate,decoration={brace,mirror,raise=2pt}] (axis cs:1,0) -- (axis cs:1,1) node [midway,right=5pt] {$r$};
            \draw [decorate,decoration={brace,mirror,raise=2pt}] (axis cs:1,-1) -- (axis cs:1,0) node [midway,right=5pt] {$r$};
        }]


        % Draw solid square
        \addplot[mark=none, thick] coordinates {(-1,-1) (1,-1) (1,1) (-1,1) (-1,-1)};
        \addplot[mark=*] coordinates {(0,0)};

        % Draw axis text
        \node at (axis cs:-1,0.5) [anchor=east] {$\mathfrak{B}_r(0) = $};

    \end{axis} 
\end{tikzpicture}
\end{document}
