function to safely add a tile

src/game.rs

@@ -199,6 +199,16 @@ impl NewTileId for Game {
     }
 }
 
+impl Game {
+    /// adds a tile safely and returns the new tile ID
+    fn add_tile(&mut self, mut tile: Tile) -> u64 {
+        let new_id = self.new_tile_id();
+        tile.id = new_id;
+        self.tiles.push(tile);
+        new_id
+    }
+}
+
 #[test]
 fn test_game_from_string() {
     let output = Game::from(
@@ -250,3 +260,14 @@ fn test_new_tile_id() {
 
     assert_eq!(game.new_tile_id(), 10);
 }
+
+#[test]
+fn test_add_tile() {
+    let mut game = mock::game_default();
+    let new_id = game.add_tile(mock::tile_default());
+    assert_eq!(new_id, 0);
+    assert_eq!(game.tiles.len(), 2);
+    let new_id = game.add_tile(mock::tile_default());
+    assert_eq!(new_id, 1);
+    assert_eq!(game.tiles.len(), 3);
+}