A recent update to the Team Fortress 2 beta gives players the ability to test out their weapons they've created for the game as Valve reveal plans to introduce more tools that will make it easier for players to contribute their own items.
User contributed items and weapons have made up a significant amount of the new items that have been added to TF2 over the past few months. Most notably, the Polycount Pack added a host of items and earned community members a nice wad of cash . Understandably, many players have been hoping to replicate their success. Many are hard at work creating their own items for the game, but have been forced to resort to hacks and workarounds in order to see their items in action. With some help from the recently added AI controlled bots, Valve have introduced map that will let players test their new models.
Full details on how the new system can be found on the Team Fortress 2 blog . Valve also mention that they're planning to release more tools in future to make creating new weapons easier. For more information on creating and submitting new items, check out the official Team Fortress 2 Contribute! page.