Add PGN exporter tests and finalize all features

Co-authored-by: mgierschdev <62764972+mgierschdev@users.noreply.github.com>

Author: Copilot

backend/src/test/java/com/backend/util/PGNExporterTest.java

@@ -0,0 +1,65 @@
+package com.backend.util;
+
+import com.backend.domain.ChessGame;
+import com.backend.models.GameState;
+import com.backend.models.Position;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Tests for PGN export functionality.
+ */
+public class PGNExporterTest {
+
+    @Test
+    public void testBasicPGNExport() {
+        ChessGame game = new ChessGame();
+        
+        // Make a few moves (opening moves)
+        game.MoveController(new Position(2, 5), new Position(3, 5)); // e2-e3 (white)
+        game.MoveController(new Position(7, 5), new Position(6, 5)); // e7-e6 (black)
+        game.MoveController(new Position(2, 4), new Position(4, 4)); // d2-d4 (white)
+        game.MoveController(new Position(7, 4), new Position(5, 4)); // d7-d5 (black)
+        
+        String pgn = game.exportToPGN();
+        
+        assertNotNull(pgn, "PGN should not be null");
+        assertTrue(pgn.contains("[Event"), "PGN should contain Event header");
+        assertTrue(pgn.contains("[Result"), "PGN should contain Result header");
+        assertTrue(pgn.contains("1."), "PGN should contain move numbers");
+        
+        // Game should still be ongoing
+        assertTrue(pgn.contains("*"), "PGN should show game ongoing with *");
+    }
+
+    @Test
+    public void testResultStringForCheckmate() {
+        String result = PGNExporter.getResultString(GameState.Checkmate, com.backend.models.Color.White);
+        assertEquals("0-1", result, "White turn at checkmate means black won");
+        
+        result = PGNExporter.getResultString(GameState.Checkmate, com.backend.models.Color.Black);
+        assertEquals("1-0", result, "Black turn at checkmate means white won");
+    }
+
+    @Test
+    public void testResultStringForDraw() {
+        String result = PGNExporter.getResultString(GameState.DrawByStalemate, com.backend.models.Color.White);
+        assertEquals("1/2-1/2", result, "Stalemate should be a draw");
+        
+        result = PGNExporter.getResultString(GameState.DrawByRepetition, com.backend.models.Color.Black);
+        assertEquals("1/2-1/2", result, "Threefold repetition should be a draw");
+        
+        result = PGNExporter.getResultString(GameState.DrawByFiftyMove, com.backend.models.Color.White);
+        assertEquals("1/2-1/2", result, "Fifty-move rule should be a draw");
+    }
+
+    @Test
+    public void testResultStringForOngoingGame() {
+        String result = PGNExporter.getResultString(GameState.Free, com.backend.models.Color.White);
+        assertEquals("*", result, "Ongoing game should show *");
+        
+        result = PGNExporter.getResultString(GameState.Check, com.backend.models.Color.Black);
+        assertEquals("*", result, "Check state should still show game ongoing");
+    }
+}