You have probably seen message like
‘Transaction log of myDatabase is full’.

Prior to version 2008 of SQL Server we will execute statement like

BACKUP LOG MyDatabase WITH TRUNCATE_ONLY

but if you tried to execute this on SQLServer 2008, 2008R2, 2012 and 2014 you will get and error like

?Msg 155, Level 15, State 1, Line 1
‘TRUNCATE_ONLY’ is not a recognized BACKUP option.

Assuming that you know that TRUNCATE_ONLY is an dangerous option, not very usable in a live systems and that officialy and recomended way to do it is to change database recovery model from FULL to SIMPLE still you can save a lot of time, space and headaches on test systems, on SQL Server 2008 and later you need to execute

BACKUP LOG MyDatabase
TO DISK = 'nul:' WITH STATS = 10

and magic is done. Your database log is truncated.