Great question, cause it never hit us (the T20 and ODI savy fans). To hit a six in test cricket, a batsman either has to be utterly aggressive one or on a high individual score. both the cases are quite rare..
The most number of sixes in test cricket is hit by Aussie wicket keeper Adam Gilchrist, with exactly 100 sixes from his 96 test match career. Brian Lara of West Indies finished career with 88 big ones while surprize package is former Kiwi allrounder Chris Cairns with 87 hits over the baundary. Vivian Richards of West Indies and Virendra Sehwag of India have hit 84 sixes in test match career but English allrounder Andrew Flintoff was fast rising up the ladder with 82 sixes from only 79 tests before he quit the longest format of cricket. here's the list..
Most sixes in test career
100 sixes = Adam Gilchrist of Australia, 96 tests.
88 sixes = Brian Lara of West Indies, 131 tests.
87 sixes = Virender Sehwag of India, 91 tests.
87 sixes = Chris Cairns of New Zealand, 62 tests.
86 sixes = Jacques Kallis of South Africa, 146 tests.
84 sixes = Vivian Richards of West Indies, 121 tests.
82 sixes = Andrew Flintoff of England, 79 tests.
82 sixes = Mathew Hayden of Australia, 103 tests.
75 sixes = Chris Gayle of West Indies, 91 tests.
73 sixes = Ricky Ponting of Australia, 155 tests.
70 sixes = Clive Llyod of West Indies, 110 tests.