Out of 44 test matches completed this year, only 4 have been decided by a margin of less than 40 runs or less than 4 wickets. 4/44 is less than one in ten.
Even the above is a little misleading, as most decided matches have been decided by huge margins, where there has been only one team having any chance of win.
Here are the above 4 matches:
New Zealand v West Indies - 1st Test Eden Park (09/03/2006) - New Zealand Won by 27 Runs
South Africa v Australia - 3rd Test New Wanderers Stadium (31/03/2006) - Australia Won by 2 Wickets
Surprise Entry Bangladesh v Australia - 1st Test Narayanganj Osmani Stadium (09/04/2006) - Australia Won by 3 Wickets
Sri Lanka v South Africa - 2nd Test P Saravanamuttu Stadium (04/08/2006) - Sri Lanka Won by 1 Wicket