what is this IMP testing you speak of?

If you know what impromptu means, it'll make a lot more sense.

Most of the time it's when we decide to test some maps in the chat room, then someone hosts it.

It means people who obsessively hang out in the Steam chat occasionally say, "Hey, we've got some maps that people want tested; let's pop up an event and get people in the server." And then they do. I never figured out how to get your map into one without either also obsessively hanging out in the chat or asking to tack yours on to the end after one has already started.

Go to the steam group and look at chat. We talk about stuff(usually not even related to mapping). If enough people have maps they want tested, we can fire up the ol' server and get a test going. Also, if you join the group, you get messages every time we are having a test.

also it's spelled impromptu

http://www.merriam-webster.com/dictionary/impromptu
Originally we had impromptu (adj) map tests. Over the years it has sorta morphed more towards impromptu (n) map tests. Which people then got lazy about and called imp.

Sometimes they're created rather quickly. Other times someone will mention it and it could be an hour or two before one starts. Just depends. Best bet is to hop into chat and ask around to see if they can run your map.

If you're having trouble finding the chat, there's a link at the top of this page. Another way of getting there is to join this group and then hop into the chat from your 'Friends' list on Steam.