Add and fix tests for the Serializers.

src/main/java/ch/fritteli/maze/generator/algorithm/Wilson.java

@@ -86,6 +86,21 @@ public class Wilson extends AbstractMazeGeneratorAlgorithm {
         direction = determineDirectionForDigging(maze.getEnd());
         t = maze.getEndTile();
         this.digTo(t, direction);
+        // seal all walls, mark all as visited
+        for (int x = 0; x < maze.getWidth(); x++) {
+            for (int y = 0; y < maze.getHeight(); y++) {
+                maze.getTileAt(x, y).forEach(tile -> {
+                    Stream.of(Direction.values())
+                            .forEach(d -> {
+                                if (tile.hasWallAt(d)) {
+                                    tile.preventDiggingToOrFrom(d);
+                                } else {
+                                    tile.digFrom(d);
+                                }
+                            });
+                });
+            }
+        }
     }
 
     @Nullable