单元测试未涵盖 LINQ `Any`

Question

I've got this method:

/// <summary>
/// Moves piece to location, does not verify that this is a valid move
/// </summary>
/// <param name="dest"></param>
public virtual void Move(Coordinate dest)
{
    if (Board.IsPieceAtLocation(dest))
    {
        if (GetAllPossibleKills().Any(p => p.BoardLocation == dest))
        {
            Board.KillPieceAtLocation(dest);
        }
        else
        {
            throw new LocationOccupiedException("Board location already occupied and kill is not valid",this, Board.GetPieceAtLocation(dest));
        }
    }
    BoardLocation = dest;
}

And it's covered by two unit tests:

[Test]
public void LocationOccupiedTest()
{
    Board board = new Board();
    board.GenerateNewGamePieces();
    Assert.Throws<LocationOccupiedException>(()=>board.GetKing(false).Move(new Coordinate(0,0)));
}

[Test]
public void KillPieceTest()
{
    Board board = new Board();
    board.GenerateNewGamePieces();
    Piece knight = board.GetPieceAtLocation(new Coordinate(1, 0));
    knight.Move(new Coordinate(1,4));
    Assert.DoesNotThrow(()=>knight.Move(new Coordinate(0,6)));
}

According to the coverage analysis, the whole method is covered except for:

if (GetAllPossibleKills().Any(p => p.BoardLocation == dest))

You can see the coverage status next to each line of code:

I don't understand how that can be the case given both branches of the if statement are traversed.

How can I get this covered?

Answer 1

I suspect the issue is that you are not testing all possible execution paths for the Any .

You may need to add extra test cases to ensure you cover (for example) moving illegally when there are other valid targets (thanks for the example @Persistence).

---

To fix this specific example, you'd need to add a test case for moving to an occupied space that isn't a valid kill target when there are other valid kill targets.

[Test]
public void MoveToOccupiedWithOtherValidTargets()
{
    Board board = new Board();
    board.GenerateNewGamePieces();
    Piece king = board.GetKing(true);
    king.Move(new Coordinate(0,5));
    board.GetPieceAtLocation(new Coordinate(0,1)).Move(new Coordinate(0,4));
    Assert.Throws<LocationOccupiedException>(()=>king.Move(new Coordinate(0,4)));
}