How To Check If You Have The Command

For example, to assume you have the command svn and you don't have the command svn1:

which svn >&/dev/null
if [ $? == 0 ]; then
  echo You have svn
fi

which svn1 >&/dev/null
if [ $? == 1 ]; then
  echo You don\'t have svn1
fi