UTests pass with Pathfinder2D

Gameboard.ShogiUI.BoardState/Piece.cs

@@ -1,9 +1,11 @@
-using System.Diagnostics;
+using PathFinding;
+using System.Collections.Generic;
+using System.Diagnostics;
 
 namespace Gameboard.ShogiUI.BoardState
 {
   [DebuggerDisplay("{WhichPiece} {Owner}")]
-  public class Piece
+  public abstract class Piece : IPlanarElement
   {
     public WhichPiece WhichPiece { get; }
     public WhichPlayer Owner { get; private set; }
@@ -48,7 +50,7 @@ namespace Gameboard.ShogiUI.BoardState
         : WhichPlayer.Player1;
     }
 
-    public void Promote() => IsPromoted = true;
+    public void Promote() => IsPromoted = CanPromote;
 
     public void Demote() => IsPromoted = false;
 
@@ -57,5 +59,11 @@ namespace Gameboard.ShogiUI.BoardState
       ToggleOwnership();
       Demote();
     }
+
+    public abstract ICollection<Path> GetPaths();
+
+    public abstract Piece DeepClone();
+
+    public bool IsUpsideDown => Owner == WhichPlayer.Player2;
   }
 }