Thanks

Your solution is wrong, check the first block:

 [[2, 4,...
  [4, 3,...

it's missing the 1

The 2x2 blocks should also contain the numbers 1-4.

for [[2, 0, 0, 1],
[0, 0, 1, 0],
[0, 2, 0, 0],
[0, 0, 0, 4]]
I have this response :
Expected: 'This sudoku is unsolvable!',
instead got: [[2, 4, 3, 1],
[4, 3, 1, 2],
[1, 2, 4, 3],
[3, 1, 2, 4]]
what am I missing here?
and there are also some random tests with the same problem.