update: Adding inner box checks to Sudoku

[TheMj0ln1r]

Current Sudoku test cases are not explicitly checking the inner box checks of the solution.

Valid Inner Boxes

Question:          Solution:
[1, 0, 0, 0]      [1, 4, 3, 2]
[0, 2, 0, 0]      [3, 2, 1, 4]
[0, 0, 3, 0]      [4, 1, 3, 2]
[0, 0, 0, 4]      [2, 3, 4, 1]

Box 0 (top-left):     Box 1 (top-right):
[1, 4]                [3, 2]
[3, 2]                [1, 4]
Values: {1,2,3,4} ✓   Values: {1,2,3,4} ✓

Box 2 (bottom-left):  Box 3 (bottom-right):
[4, 1]                [3, 2]
[2, 3]                [4, 1]
Values: {1,2,3,4} ✓   Values: {1,2,3,4} ✓

Invalid Inner Boxes

Question:          Solution:
[1, 0, 0, 0]      [1, 2, 3, 4]
[0, 1, 0, 0]      [2, 1, 4, 3]
[0, 0, 1, 0]      [3, 4, 1, 2]
[0, 0, 0, 1]      [4, 3, 2, 1]

Box 0 (top-left):     Box 1 (top-right):
[1, 2]                [3, 4]
[2, 1]                [4, 3]
Values: {1,2,2,1} - Invalid ; Values: {3,4,4,3}  - Invalid

Box 2 (bottom-left):  Box 3 (bottom-right):
[3, 4]                [1, 2]
[4, 3]                [2, 1]
Values: {3,4,4,3} - Invalid   Values: {1,2,2,1} - Invalid

Because of no such test case to check inner boxes the invalid sudoku will still pass the test.

This makes sudoko a bit more hard puzzle, a good challenge for solvers