Thank you for your reply. Actually, I had realized the point, after a while I wrote this issue. No problem, now :)

I think you could misinterpret the logs. There are two test cases with size 1x1, one of them is valid and expects true, and one is invalid and expects false. Checking just for length is not enough, You have to check what's inside of the grid.

It would be great if the instructions of the question were explained clearly for the people who don't know what Sudoku is. For example, instead of saying that "Rows may only contain integers", I recommend that the uniqueness of the integers must be mentioned in that sentence clearly.