Good Day. I`ve posted some 'wrong' solution in order to check test coverage. So my solution, that check only '0'-sum diagonals passed successfully, but I guess it`s wrong. E.g.:

           [[0,   1,  2,  1],
            [-1,  0,  3,  3],
            [-2, -1,  0,  3],
            [-3, -3, -3,  0]]

Please, see diagonal 1, 3, -1, -3. So my "wrong" code will "say" that this matrix "skew-symmetric matrix", but it`s not. And your tests do not coverage this test-case.