You can define an uppercase
style, similar to the definitions used by standard, but including \MakeUppercase
(\uppercase
in case hyperref
is loaded):
\documentclass[fontsize=12pt]{scrreprt}
\usepackage{tocstyle}
\makeatletter
\newtocstyle{uppercase}{%
\settocfeature{dothook}{\normalfont}%
\settocfeature[0]{entryhook}{\bfseries\MakeUppercase}
\settocfeature[1]{entryhook}{\MakeUppercase}%
\settocfeature[2]{entryhook}{\MakeUppercase}%
\settocfeature[-1]{entryvskip}{2.25em plus 1pt}%
\settocfeature[-1]{leaders}{\hfill}%
\settocfeature[0]{entryvskip}{1em plus 1pt}%
\settocfeature[0]{leaders}{\hfill}%
\iftochaschapter\else
\settocfeature[1]{entryvskip}{1em plus 1pt}%
\settocfeature[1]{leaders}{\hfill}%
\settocfeature[1]{entryhook}{%
\begingroup
\edef\@tempa{toc}%
\ifx\tocstyleAliasTOC\@tempa\aftergroup\bfseries\fi
\endgroup
}%
\fi
}
\makeatother
\usetocstyle{uppercase}
\addtokomafont{disposition}{\rmfamily}
\usepackage{titlesec}
\usepackage{setspace}
\renewcommand{\thechapter}{\Roman{chapter}}
\renewcommand \thesection{\arabic{chapter}.\arabic{section}}
\renewcommand \thesubsection{\arabic{chapter}.\arabic{section}.\arabic{subsection}}
\titleformat{\chapter}[display] {\singlespacing\rmfamily\fontsize{16pt}{19pt}\bfseries}
{\MakeUppercase{\chaptertitlename\ \thechapter}\filcenter}{10pt}{\centering\uppercase}
{\fontsize{14pt}{16pt}\filcenter}
\begin{document}
\tableofcontents
\newpage
\chapter{Test}
\section{Test}
\subsection{Test}
\chapter{Test}
\section{Test}
\chapter{Test}
\section{Test}
\end{document}
By the way,using titlesec
with KOMA classes might not be the best option; see Incompatibilities between KOMA-Script and titlesec.
I know that perhaps you are dealing with a Faculty requirement for your thesis, but having titles and ToC entries in upper case is not the best typographical choice; at this respect, the KOMA documentation says (referring to headers, but the same can be applied to other elements):
Unfortunately LaTeX's command for upper case letter typesetting,
\MakeUppercase
results in an very inadequate typesetting, because it
neither uses letter spacing nor does it space balancing. One reason
for this behaviour might be, that a glyph analyzing would be needed,
to incorporate the letter shapes and their combination while space
balancing. Because of this KOMA-Script author suggests to abstain from
upper case letter typesetting for running heads.