How to test two objects in xunit using FluentAssertions

Question

I have a Matrix class, and another class which is using that matrix changing it a little bit. I'd like to test both matrix, one from the matrix class and the other one which has been changed, so I can confirmed they're not the same.

Something like this.

[Fact]
public void MatrixFromMatrixIsntTheSameThanMatrixFromMineSweeper()
{
    Matrix _matrix = new Matrix(4, 4);
    MineSweeper mineSweeper = new MineSweeper(4, 4, 2);

    mineSweeper.Matrix.Should().NotBe(_matrix);
}

The thing is that Be/NotBe seems is using the reference from the object, so always it returns false because they're not the same. I also have tried with NotBeSameAs, NotBeEquivalentTo.

These are the Matrix and MineSweeper class.

Matrix Class

public struct Coordinate
{
    public int X;
    public int Y;

    public Coordinate(int x, int y)
        => (X, Y) = (x, y);
}

public class Matrix
{
    private readonly int _M, _N;
    private readonly Cell[,] _matrix;
    private const char InitValue = '.';

    public Matrix(int m,  int n)
    {
        (_M, _N) = (m, n);
        _matrix = new Cell[m, n];
        Initialize();
    }

    private void Initialize()
    { 
        for (int m = 0; m < _M; m++)
            for (int n = 0; n < _N; n++)
                _matrix[m, n] = new Cell(InitValue);
    }

    public Cell At(Coordinate coordinate) 
        => _matrix[coordinate.X, coordinate.Y];
    
    public void SetMine(Coordinate coordinate)
    { 
        _matrix[coordinate.X, coordinate.Y] = new Cell('*');
    }
}

MineSweeper Class

public class MineSweeper
{
    private readonly int _m, _n, _numMines;
    public Matrix Matrix { get; }

    public MineSweeper(int m, int n, int numMines)
    {
        (_m, _n, _numMines) = (m, n, numMines);
        Matrix = new Matrix(m, n);
        SetMines();
    }

    private void SetMines()
    {
        HashSet<Coordinate> minesSet = new HashSet<Coordinate>();
        Random rnd = new Random();

        while (minesSet.Count != _numMines)
            minesSet.Add(new Coordinate(rnd.Next(0, _m), rnd.Next(0, _n)));

        foreach (Coordinate coordinate in minesSet)
            Matrix.SetMine(coordinate);
    }
}

Answer 1

Normally we recommend BeEquivalentTo, but since your Matrix class doesn't expose any public fields or properties, the only other option is what NPras suggested in option 2.