单元测试和集成测试之间的界限在哪里（例如）？

Question

I have a problem in understanding where is (or should be) a line between those two kind of tests. So, I have a dummy example: A simple tic-tac-toe game. The game has its own board (3x3) with 9 cells. Dependencies are obvious: Game <- Board <- Cell .

Quick description: Every time user click "New Game" , the new Game is created (by GameFactory) and Board needs to be cleared/reset. In the entire lifetime of GameFactory there there is single object of Board. Reset the Board means to create brand new Cell objects. Here is the code:

GameFactory: (as you can see I created Board once, so I need to reset it in Game constructor):

public class GameFactory : IGameFactory
{
    private readonly IBoard board;
    public GameFactory(IBoard board)
    {
        this.board = board;
    }
    public IGame Create()
    {
        return new Game(board);
    }
}

Cell and CellFactory

public interface ICell
{
    int PlayerId { get; set; }
    int Row { get; set; }
    int Column { get; set; }
}

public interface ICellFactory
{
    ICell Create(int row, int column);
}

public class CellFactory : ICellFactory
{
    public ICell Create(int row, int column)
    {
        return new Cell(row, column);
    }
}

and finally, Board :

public interface IBoard
{
    int Width { get; }
    int Height { get; }

    void Reset();

    // Rest is not important for that question
    // ... 
}

public class Board : IBoard
{
    private ICell[,] cells;
    private readonly ICellFactory cellFactory;

    public int Width { get; }
    public int Height { get; }

    public void Reset()
    {
        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] = cellFactory.Create(i, j);
            }
        }
    }

    // Rest is not important for that question
    // ...
}

The Question: How can I test Reset method in Board object? Board is independent from the Game, but it has its own Cells and CellFactory.

Few additional questions related: - Is it possible to create Board unit tests? Can I say that, if an object depends on other objects (even if they are interfaces) then it's already has to be integration test, not unit test?

Here is test I made already. (Reset is called in Board constructor):

    [Test]
    public void BoardCreationTest()
    {
        var cellFactory = new CellFactory();
        IBoard board = new Board(3, 3, cellFactory);

        for (int i = 0; i < board.Height; i++)
        {
            for (int j = 0; j < board.Width; j++)
            {
                // Check if board.cells[i,j].PlayerId is zero (it has to be zero, player zero is empty cell)
                // Another thing is that cells are private, cause project doesn't need it public
                // Should I make cells public just for tests?

                // Right now I'm checking it IsMoveValid(column, row, playerId)
                // It has to be true, when player 1 wants move in certain cell (it has to be zero, player zero is empty cell)
                Assert.IsTrue(board.IsMoveValid(i, j, 1));
            }
        }
    } 

EDIT: Board constructor:

    public Board(int width, int height, ICellFactory cellFactory)
    {
        Width = width;
        Height = height;
        this.cellFactory = cellFactory;

        Reset();
    }

EDIT2: My whole test now. It passes:

[TestFixture]
class BoardTests
{
    private IBoard board;

    [SetUp]
    public void RunBeforeAnyTests()
    {
        var cellFact = Substitute.For<ICellFactory>();
        cellFact.Create(Arg.Any<int>(), Arg.Any<int>())
            .Returns(x => new Cell((int)x[0], (int)x[1]));
        board = new Board(3, 3, cellFact);
    }

    [Test]
    public void BoardCreationTest()
    {
        board.Reset();

        for (int i = 0; i < board.Height; i++)
        {
            for (int j = 0; j < board.Width; j++)
            {
                Assert.IsTrue(board.IsMoveValid(i, j, 1));
            }
        }
    }
}

Answer 1

You can use a simple stub for CellFactory and Cell , using NSubstitute for example. In this case you will test only Reset method logic

[Test]
public void BoardCreationTest()
{
    var board = CreateBoard();

    //Calling method explicitly makes test more readable
    board.Reset();

    for (int i = 0; i < board.Height; i++)
    {
        for (int j = 0; j < board.Width; j++)
        {
           Assert.IsTrue(board.IsMoveValid(i, j, 1));
        }
    }
}

private IBoard CreateBoard()
{
    var cellFactory = Substitute.For<ICellFactory>();
    //You may replace Cell with another mock or smth else. Depends on your assert section.
    cellFactory.Create(Arg.Any<int>(), Arg.Any<int>())
       .Returns(x => new Cell((int)x[0], (int)x[1]));        
    IBoard board = new Board(3, 3, cellFactory);
} 

Unit test mean that you test a single unit of logic. So replacing all dependencies with fakes, gives you ability to test only one unit of logic.