Peter Norvig wrote a sudoku solver, not by using TDD, but using old-fashioned engineering: http://norvig.com/sudoku.html

Ron Jeffries' attempts:

http://xprogramming.com/articles/sudokumusings/

http://xprogramming.com/articles/oksudoku/

http://xprogramming.com/articles/sudoku2

http://xprogramming.com/articles/sudoku4

http://xprogramming.com/articles/sudoku5

And, as dessert (Ron is very frank about his failures):

This is surely the most ignominious debacle of a project listed on my site, even though others have also not shipped. (Sudoku did not ship and will not. Shotgun will go forward if the Customer wants to.)

http://xprogramming.com/articles/roroncemore/