On va faire simple :

BOSTON ATTACK :
"Officials : There will be a controlled explosion opposite the library within one minute as part of bomb squad activities" @bostonglobe 15th april 2013

WAR GAMES ON SEPTEMBER 11TH
On the very morning of 9/11/01, five war games and terror drills were being conducted by several U.S. defense agencies, including one « live fly » exercise using REAL planes. Then-Acting Head of the Joint Chiefs of Staff, Air Force General Richard B. Myers, admitted to 4 of the war games in congressional testimony — see transcript here or video here (6 minutes and 12 seconds into the video).
Norad had run drills for several years of planes being used as weapons against the World Trade Center and other U.S. high-profile buildings, and "numerous types of civilian and military aircraft were used as mock hijacked aircraft". In other words, drills using REAL AIRCRAFT simulating terrorist attacks crashing jets into buildings, including the twin towers, were run. See also official military website showing 2000 military drill, using miniatures, involving a plane crashing into the Pentagon.
Indeed, a former Los Angeles police department investigator, whose newsletter is read by 45 members of congress, both the house and senate intelligence committees, and professors at more than 40 universities around the world, claims that he obtained an on-the-record confirmation from NORAD that ON 9/11, NORAD and the Joint Chiefs of Staff were conducting a joint, live-fly, hijack exercise which involved government-operated aircraft POSING AS HIJACKED AIRLINERS.

LONDON BOMB ATTACK
Amazingly, on the morning of July 7th 2005,a UK-based crisis management firm, Visor Consultants, was running terror drills that simulated bomb attacks at the very same train stations as the actual bombings.