Currently SVN fixture file at arcanist/src/repository/api/__tests__/state/svn_basic.svn.tgz path is in SVN 1.7 format. This makes it impossible to run unit tests if installed SVN version is 1.6.
I guess SVN version needs to be checked to call svn upgrade only when SVN is > 1.6, because there was no such command in SVN 1.6 or below.
Unfortunately it's one way trip, because if I update SVN then I also need to update all my working copies in 1.6 format to make them compatible. And I will then hit known SVN 1.7 bug with SQLLite database (that's what lives in .svn folders now) locking over Samba/NFS mounted drives (when several programs are attempting to access same working copy at same time and only one will succeed).
I guess your team has SVN 1.7 installed on your development machines so you can't really open SVN 1.6 working copy without upgrading it to 1.7 format.