Testing for a sudoku

I'm currently / was programming a proframm which tests if the given sudoku is a real sudoku. It works. My only problem is that i dont know if it meets all the required criteria. I am testing that every number is 9x in the sudoku and that it is only 1x in every 3x3 field. Adding to that im testing that every vertical and horizontal line (when added together) have the same result(45) wich includes that the overall result has to be 405. My question is if I need to test for every number to only once in every horizontal and vertical line once or is it not needed anymore?