Promotions should work now.

chess/board_test.go

@@ -145,7 +145,7 @@ func Test_CheckMove_validPromotion(t *testing.T) {
 
 	board.position[types.Coordinate{Col: 7, Row: 7}] = King{Color: types.Black}
 
-	shortName := types.QueenShortName
+	shortName := types.QueenShortName.String()
 	move := types.Move{
 		StartSquare:      types.Coordinate{Col: 1, Row: 7},
 		EndSquare:        types.Coordinate{Col: 1, Row: 8},
@@ -192,19 +192,19 @@ func Test_CheckMove_HistoryWorks(t *testing.T) {
 		{
 			StartSquare: types.Coordinate{Col: 1, Row: 2},
 			EndSquare:   types.Coordinate{Col: 1, Row: 3},
-			PieceMoved:  'p',
+			PieceMoved:  "p",
 			ColorMoved:  "white",
 		},
 		{
 			StartSquare: types.Coordinate{Col: 3, Row: 7},
 			EndSquare:   types.Coordinate{Col: 3, Row: 5},
-			PieceMoved:  'p',
+			PieceMoved:  "p",
 			ColorMoved:  "black",
 		},
 		{
 			StartSquare: types.Coordinate{Col: 1, Row: 3},
 			EndSquare:   types.Coordinate{Col: 1, Row: 4},
-			PieceMoved:  'p',
+			PieceMoved:  "p",
 			ColorMoved:  "white",
 		},
 	}

chess/pawn.go

@@ -40,7 +40,7 @@ func (p *Pawn) HandlePossiblePromotion(b *Board, move types.Move) bool {
 	messageContainsPromotion := move.IsPromotionMove()
 
 	if messageContainsPromotion {
-		promotionToPiece = *move.PromotionToPiece
+		promotionToPiece = types.PieceShortName(*move.PromotionToPiece)
 	}
 
 	switch move.ColorMoved {

chess/piece_interface.go

@@ -14,17 +14,17 @@ func GetPieceForShortName(name types.PieceShortName, color types.ChessColor) Pie
 	var piece Piece
 
 	switch name {
-	case 'p':
+	case "p":
 		piece = Pawn{Color: color}
-	case 'q':
+	case "q":
 		piece = Queen{Color: color}
-	case 'k':
+	case "k":
 		piece = King{Color: color}
-	case 'b':
+	case "b":
 		piece = Bishop{Color: color}
-	case 'r':
+	case "r":
 		piece = Rook{Color: color}
-	case 'n':
+	case "n":
 		piece = Knight{Color: color}
 	}
 	return piece
@@ -34,17 +34,17 @@ func GetShortNameForPiece(piece Piece) types.PieceShortName {
 	var name types.PieceShortName
 	switch piece.(type) {
 	case Pawn:
-		name = 'p'
+		name = "p"
 	case Queen:
-		name = 'q'
+		name = "q"
 	case King:
-		name = 'k'
+		name = "k"
 	case Bishop:
-		name = 'b'
+		name = "b"
 	case Rook:
-		name = 'r'
+		name = "r"
 	case Knight:
-		name = 'n'
+		name = "n"
 	}
 	return name
 }

types/move.go

@@ -3,9 +3,9 @@ package types
 type Move struct {
 	StartSquare      Coordinate `json:"startSquare"`
 	EndSquare        Coordinate `json:"endSquare"`
-	PieceMoved       PieceShortName
+	PromotionToPiece *string    `json:"promotionToPiece,omitempty"`
 	ColorMoved       ChessColor
-	PromotionToPiece *PieceShortName `json:"promotionToPiece,omitempty"`
+	PieceMoved       PieceShortName
 }
 
 func (m Move) IsPromotionMove() bool {

types/shortname.go

@@ -1,12 +1,16 @@
 package types
 
-type PieceShortName rune
+type PieceShortName string
 
 const (
-	PawnShortName   PieceShortName = 'p'
-	RookShortName   PieceShortName = 'r'
-	KnightShortName PieceShortName = 'n'
-	BishopShortName PieceShortName = 'b'
-	QueenShortName  PieceShortName = 'q'
-	KingShortName   PieceShortName = 'k'
+	PawnShortName   PieceShortName = "p"
+	RookShortName   PieceShortName = "r"
+	KnightShortName PieceShortName = "n"
+	BishopShortName PieceShortName = "b"
+	QueenShortName  PieceShortName = "q"
+	KingShortName   PieceShortName = "k"
 )
+
+func (p PieceShortName) String() string {
+	return string(p)
+}