LaTeX3 - Test string equality + Star version

I'm looking for some good advice on switching from (La)TeX to LaTeX3

Here is the first questions corresponding to the toy code below.

1. What is a good way to manage an optional argument with LaTeX3?

2. What is a good way to define star versions with LaTeX3?

\documentclass[12pt,a4paper]{article}\usepackage{ifthen}\makeatletter\newcommand\test{\@ifstar{\@test@star}{\@test@no@star}}\newcommand\@test@no@star[1]{%    I am a %    \ifthenelse{\equal{#1}{upper}}%               {TSAR}%               {tsar}%    .}\newcommand\@test@star{%    I am a star.%}\makeatother\begin{document}\test{}\test{upper}\test*{}\end{document}