Bash – Get Parent Directory

bashdirectorydirname

If I have a file path such as…

/home/smith/Desktop/Test
/home/smith/Desktop/Test/

How do I change the string so it will be the parent directory?

e.g.

/home/smith/Desktop
/home/smith/Desktop/

dir=/home/smith/Desktop/Test
parentdir="$(dirname "$dir")"

Works if there is a trailing slash, too.