If like me, you don't have a beta key, and you are too much impatient to test the new units of heart of the swarm, this tutorial might interest you !
This is a proof that this tutorial works:
1) You have to download and install the HOTS client.
2) You have to download and extract to somewhere the HOTS modified maps.
2b) If you already know how to use the map editor, you can already play and enjoy ^^. For the others, from this point, the tutorial will take 5 minutes ^^.
3) Open the Starcraft II Beta - Map Editor.
4) Open one of the two HOTS modified maps.
4b) Click yes when the dependency data box appears:
5) Adjust the player properties (e.g. select your race or set a computer).
6) Adjust the preferences (e.g. game speed).
7) Launch the game by testing the document.
8) If an error appears during the game, uncheck the corresponding box.
9) Enjoy !!
9b) AI is set to very easy for the moment ... but you can test all the new units.
10) All the credits go to Vernam7. If you want to use his alternative method, go to this thread:
11) If this tutorial works for you and you like it, please post a comment. It is always nice to get some feedback and to spread information ^^.