documentclass{report}
begin{document}
tableofcontents
clearpage
chapter{TEST}
section{Introduction}
section{Test section one}
subsection{Test subsection}
subsection{Test subsection}
subsubsection{Test subsubsection}
subsection{Test subsection}
end{document}

documentclass{report}
%%%%%ADDED CODE%%%%%
usepackage{titletoc}%
titlecontents{chapter}% <section-type>
  [0pt]% <left>
  {bfseries}% <above-code>
  {chaptername thecontentslabel:quad}% <numbered-entry-format>
  {}% <numberless-entry-format>
  {hfillcontentspage}% <filler-page-format>
%%%%%%END OF ADDED CODE%%%%%

begin{document}
tableofcontents
clearpage
chapter{TEST}
section{Introduction}
section{Test section one}
subsection{Test subsection}
subsection{Test subsection}
subsubsection{Test subsubsection}
subsection{Test subsection}
end{document}

usepackage[titles]{tocloft}
renewcommandcftchappresnum{Chapter }
renewcommandcftchapaftersnum{:}
newlengthmylen
settowidthmylen{bfseries Chapter 1: } % if more than 9 chapters, use "Chapter 10"
cftsetindents{chap}{0pt}{mylen}

documentclass{report}

usepackage[titles]{tocloft}
renewcommandcftchappresnum{Chapter }
renewcommandcftchapaftersnum{:}
newlengthmylen
settowidthmylen{bfseries Chapter 1: }
cftsetindents{chap}{0pt}{mylen}

begin{document}
tableofcontents

chapter{TEST}
section{Introduction}
section{Test section one}
subsection{Test subsection}
subsection{Test subsection}
subsubsection{Test subsubsection}
subsection{Test subsection}
end{document}