Thank you so much !!!

[5, 3, 4,  6, 7, 8,  9, 1, 2],
[6, 7, 2,  1, 9, 5,  3, 4, 8],
[1, 9, 8,  3, 4, 2,  5, 6, 7],

[8, 5, 9,  7, 6, 1,  4, 2, 3],
[4, 2, 6,  8, 5, 3,  7, 9, 1],
[7, 1, 3,  9, 2, 4,  8, 5, 6],

[9, 6, 1,  5, 3, 7,  2, 8, 4],
[2, 8, 7,  4, 1, 9,  6, 3, 5],
[3, 4, 5,  2, 8, 6,  1, 7, 9]

Those are the 9 sub-squares, the one you picked isn't one of them.

So I searched for that and I found: Each of the 9 sub-squares, of size 3x3, contains a unique value from 1-9.
This is what I mean, there for that square is not valid. So why should I get true ??
Thanks!

Please follow the link to Wikipedia to see an example of sudoku board and what a valid "sub grid" is. Not every 3x3 square of the board is a subgrid where the rules apply, there's only 9 of them.

Hi
looking at the test:
Test.assertEquals(validSolution([
[5, 3, 4, 6, 7, 8, 9, 1, 2],
[6, 7, 2, 1, 9, 5, 3, 4, 8],
[1, 9, 8, 3, 4, 2, 5, 6, 7],
[8, 5, 9, 7, 6, 1, 4, 2, 3],
[4, 2, 6, 8, 5, 3, 7, 9, 1],
[7, 1, 3, 9, 2, 4, 8, 5, 6],
[9, 6, 1, 5, 3, 7, 2, 8, 4],
[2, 8, 7, 4, 1, 9, 6, 3, 5],
[3, 4, 5, 2, 8, 6, 1, 7, 9]]), true);

According to the definitions, every sub grid 3X3 should contain 1-9 digits.
As far as I see, please look at the sub grid starting on position [0, 2] - the number 4
See that it's missing number 5:
4,6,7
2,1,9
8,3,4
Maybe I miss something.
Thanks