public void Can_calculate_index_at_row_from_node_index(uint row, ulong nodeIndex, uint?indexAtRow)
 {
     if (indexAtRow == null)
     {
         Assert.Throws <ArgumentOutOfRangeException>(() => BaselineTree.GetIndexAtRow(row, nodeIndex));
     }
     else
     {
         BaselineTree.GetIndexAtRow(row, nodeIndex).Should().Be(indexAtRow.Value);
     }
 }