Globe described playtesting as "what everyone says is the least favorite part of the game-building operation". Steve Meretzky of Infocom said that "the first part of debugging is exciting; it's the first feedback. Somebody is actually playing your game. But by the end, you get sick of the little problems. You have spent three months inventing the game, and now you have to spend just as much time cleaning it up". The requirements for a person to be considered for participation in a playtest vary. Some playtests are open to anyone willing to volunteer, while others specifically target professional gamers and journalists. Some playtests also try to evaluate the game's appeal to players with different levels of experience by selecting players with varying exposure to the game's genre. An example of a video game that made extensive use of open playtesting is Minecraft, which was made available for purchase in its pre-alpha stages. This both helped to financially support the game and provide feedback and bug testing during its early stages. Playtesting began even before the game features included multiplayer or the ability to save games. Mojang continues to make use of playtesting with Minecraft through weekly development releases, allowing players to experiment with unfinished additions to the game and provide feedback on them. Some games make use of playtesting with only part of their content, leaving other important sections unexposed to the public. StarCraft II: Heart of the Swarm was tested in this manner; its playtest only included the multiplayer portion of the game, while the single-player campaign was not revealed. Heart of the Swarm is also an example of a playtest where average players are not being considered for entry; the initial wave of testers are only being selected from the ranks of professional SCII gamers and from the media. The open-source video game engine remake OpenRA, which recreates the early Command & Conquer games, publishes playtests to the public during the release process so that a broader range of testers can verify that new features don't introduce critical errors such as desync problems in the lockstep protocol and unwanted side effects on the gameplay can be balanced out prior to the next stable release. Team Fortress 2 uses a method of playtesting whereby players that purchased the game can participate in an open beta. The beta is nearly identical to the actual game itself, but includes items