For those of you that don't know how to do this, I figure I'll make a small tutorial (as requested).
Let's just say you'd like to run around a map by yourself. Great for learning where guns,health and armor spawns. Or how to do objectives in maps you don't know. There's 2 ways you can do this.
#1) In zps, go to the "create server" option, instead of "find server". This will open a small UI (user interface) that has a few options for your little test server. You can name your server, pick how many allowed to join and so on. 1 thing you should have checked on is the testmode option. this will allow you to run around the map on your own.
Then you pick a map from a list of maps. This list is out of all the maps you have in your Program Files\Valve\Steam\SteamApps\yoursteamaccountname\zombie panic! source\zps\maps folder. Might be a little different path for vista and windows 7. I have XP.... Anyways if you were to download a new map, you would place the "bsp" file in this folder. After you picked a map create your server and have some fun testing.
#2) This is the more macho way to do it. Open up console (I'm guessing every1 here knows how to do this). For most console commands it's 1 to turn on and 0 to turn off.
Console commands:map zpo_mapnamehere
This loads the map you want. You have to replace the map name with the actual map you want.sv_testmode 1
Turns testmode on so you can run around the map.sv_testmode 0
Turns testmode off, and by doing this restarts the round. Have to turn on testmode again to play again.net_graph 1
Turns on graph mode so you can see the frames per second (fps).sv_cheats 1
Turns on cheats mode so you may enter other commands.
While sv_cheats is on:buhda 1
Turns on god mode so you will still take damage, but stop at 1hp.noclip 1
Allows you to pass through walls.
These next few commands are used while cheats are on, but are more for developers for maps:ent_messages_draw 1
Shows you which entities that are firing on screen.mat_wireframe 1
Turns on wire frame mode so you may see through walls and see if the whole map is being rendered (which is bad for frame rates).mat_leafvis 1
Allows you to see the visleaves in the map. (red boxes that represent visibility carved out by a levels world brush geometry).+showbudget
turns on -showbudget
This shows with a graph whats being used in each area you stand in. Good for testing optimization.
There's many many more commands, but these are great for testing maps. Hope this helps a little. Thanks for reading.