/// <summary>
        /// This method will return the list of cells that meet the specification.
        /// <param name="cell"> source cell, whose neighbours need to find </param>
        /// <param name="specification">Actual specification, which need to pass by neighbours.  </param>
        /// <returns>return the cell collection which pass the specification. </returns>
        public ICollection<Cell> FindNeighbourCells(Cell cell, ISpecification<Cell> specification)
        {
            if(cell == null)
                throw new ArgumentNullException("Cell can't be empty");

            List<Cell> cells = new List<Cell>();

            int startRow;
            int startCol;
            int endRow;
            int endCol;

            int colIndex = cell.ColNumber;
            int rowIndex = cell.RowNumber;

            GetValidStartRowAndCol(rowIndex, colIndex, out startRow, out startCol);
            GetValidEndRowAndCol(rowIndex, colIndex, out endRow, out endCol);

            for (int xcoord = startRow; xcoord <= endRow; xcoord++)
            {
                for (int ycoord = startCol; ycoord <= endCol; ycoord++)
                {
                    if (!(xcoord == rowIndex && ycoord == colIndex))
                    {
                        if (specification == null)
                            cells.Add(grid[xcoord, ycoord]);
                        else
                            if (specification.IsSpecificationMeet(grid[xcoord, ycoord]))
                                cells.Add(grid[xcoord, ycoord]);
                    }
                }
            }
            return cells;
        }