Verifying private class members in Unit Testing

This code is an academic example. I was trying to write something easy because the domain is not important but the principles and best practices.

In this code, I have a class - Table. It has a private array (of objects Cell), which is used by many public functions in the code but there is no function that will return a particular cell. So the problem I have, is how can I test the Reset function? I can call this function but I can't review its result especially with the Option 2 where I don't have any references to this array.

That got me thinking if the design is correct.. and that lead me here.

My questions are:

• Do I violate any SOLID principle?

• Is the option 2 better way to go? (although in that case, there's no way to test it

Here's the code:

public class Cell
{
    public int X { get; set; }
    public int Y { get; set; }
    public string Value { get; set; }
}

public class Table
{
    private Cell[,] Cells { get; }
    public Table(Cell[,] cells)
    {
        Cells = cells;
    }

    public void SetCell(int x, int y, string value)
    {
        Cells[x, y].Value = value;
    }

    public void Reset()
    {
        for (int i = 0; i < Cells.GetLength(0); i++)
        {
            for (int j = 0; j < Cells.GetLength(1); j++)
            {
                Cells[i, j].Value = "";
            }
        }
    }

    public bool AreNeighborCellsSet(int x, int y)
    {
        bool areNeighborCellsSet = false;

        // checking...

        return areNeighborCellsSet;
    }
}

Option 2:

public class Table
{
    private Cell[,] Cells { get; }

    public Table(int height, int width, ICellFactory cellFactory)
    {
        Cells = new ICell[height, width];
        for (int i = 0; i < Cells.GetLength(0); i++)
        {
            for (int j = 0; j < Cells.GetLength(1); j++)
            {
                Cells[i, j].Value = cellFactory.Create(i, j);
            }
        }
    }

    // Rest is the same
}

how can I test Reset function? I can call this function, but I can't review its result. Specially with the Option 2 where I don't have any references to this Array.

You always test only public APIs so you need to verify the results of the many public functions whether they behave they way you expect them after resetting the table.

They are your contract and their expected results you need to verify.


Is the option 2 better way to go? (although in that case, there's no way to test it

There is, the public APIs. If the initialization didn't work correctly you will get invalid results from them.


I don't have any references to this Array

This is an internal detail that could change at any time. You don't test it. You test the public contract that you usually must not change.

StackExchange Code Review Q#160791, answer score: 5