feat: update draw offer test to include draw decline scenario

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineDrawOfferTest.scala

@@ -194,7 +194,7 @@ class GameEngineDrawOfferTest extends AnyFunSuite with Matchers:
       case other =>
         fail(s"Expected InvalidMoveEvent, but got $other")
 
-  test("Draw offer is cleared when game ends by resignation"):
+  test("Draw offer is cleared when game ends by resignation (accept)"):
     val engine   = new GameEngine()
     val observer = new DrawOfferMockObserver()
     engine.subscribe(observer)
@@ -214,6 +214,26 @@ class GameEngineDrawOfferTest extends AnyFunSuite with Matchers:
       case other =>
         fail(s"Expected InvalidMoveEvent, but got $other")
 
+  test("Draw offer is cleared when game ends by resignation"):
+    val engine   = new GameEngine()
+    val observer = new DrawOfferMockObserver()
+    engine.subscribe(observer)
+
+    engine.offerDraw(Color.White)
+    observer.events.clear()
+    engine.resign(Color.Black)
+
+    // Try to accept the now-cleared draw offer
+    observer.events.clear()
+    engine.declineDraw(Color.White)
+
+    observer.events should have length 1
+    observer.events.head match
+      case event: InvalidMoveEvent =>
+        event.reason shouldBe InvalidMoveReason.GameAlreadyOver
+      case other =>
+        fail(s"Expected InvalidMoveEvent, but got $other")
+
 private class DrawOfferMockObserver extends Observer:
   val events = mutable.ListBuffer[GameEvent]()