test: fixed tests for ball contact with exit rail

lib/game/components/spaceship_exit_rail.dart

@@ -217,7 +217,7 @@ class SpaceshipExitRailEndBallContactCallback
   @override
   void begin(SpaceshipExitRailEnd exitRail, Ball ball, _) {
     ball
-      ..sendTo(1) // TODO(ruimiguel): sendTo board priority
+      ..sendTo(exitRail.outsidePriority)
       ..layer = exitRail.outsideLayer;
   }
 }

test/game/components/spaceship_exit_rail_test.dart

@@ -32,28 +32,30 @@ void main() {
     });
 
     group('SpaceshipExitHoleBallContactCallback', () {
-      test('changes the ball priority on contact', () {
+      setUp(() {
+        when(() => ball.priority).thenReturn(1);
         when(() => exitRailEnd.outsideLayer).thenReturn(Layer.board);
+        when(() => exitRailEnd.outsidePriority).thenReturn(0);
+      });
 
+      test('changes the ball priority on contact', () {
         SpaceshipExitRailEndBallContactCallback().begin(
           exitRailEnd,
           ball,
           MockContact(),
         );
 
-        verify(() => ball.priority = 1).called(1);
+        verify(() => ball.sendTo(exitRailEnd.outsidePriority)).called(1);
       });
 
-      test('reorders the game children', () {
-        when(() => exitRailEnd.outsideLayer).thenReturn(Layer.board);
-
+      test('changes the ball layer on contact', () {
         SpaceshipExitRailEndBallContactCallback().begin(
           exitRailEnd,
           ball,
           MockContact(),
         );
 
-        verify(game.reorderChildren).called(1);
+        verify(() => ball.layer = exitRailEnd.outsideLayer).called(1);
       });
     });
   });