Took some hunting to find this information so I thought I would make a post so other may not have to waste an hour.
If you wish to practise Left for Dead 2 versus mode you will have to use the following console commands:
bind "F1" "z_spawn boomer"
bind "F2" "z_spawn smoker"
bind "F3" "z_spawn hunter"
bind "F4" "z_spawn charger"
bind "F5" "z_spawn spitter"
bind "F6" "z_spawn tank"
bind "F7" "z_spawn witch"
It would be better to copy and paste that lot into a text file and name it
practice.cfg and save it within you
cfg directory. Then you would simply be able to use the command
exec practice.cfg from the console. To spawn as any give creature use the F keys as listed.
Happy wall jumping