public void isValid_Test()
{
// OutOfBound
Assert.IsFalse(Solution.isValid(-1, -1, 0, 0, 3, 3));
Assert.IsFalse(Solution.isValid(4, 2, 0, 0, 3, 3));
// Same as current position
Assert.IsFalse(Solution.isValid(0, 0, 0, 0, 3, 3));
// valid neighbor
Assert.IsTrue(Solution.isValid(1, 1, 0, 0, 3, 3));
}