public void ShouldGetSomeFlaggedCells()
        {
            _mineSweeper.Flg(1);
            _mineSweeper.Flg(7);
            _mineSweeper.Flg(9);

            var flaggedCells = _mineSweeper.GetFgdCells();

            Assert.That(flaggedCells.Count, Is.EqualTo(3));
        }