Fix tests

src/world.rs

@@ -141,8 +141,8 @@ mod test {
       vec![(Position { x: 0, y: 0 }, Box::new(NullAgent))],
     );
     world.do_step();
-    assert_eq!(world.tagged, 0);
-    assert_eq!(world.tagged_by, None);
+    assert_eq!(world.state.tagged, 0);
+    assert_eq!(world.state.tagged_by, None);
   }
 
   #[test]
@@ -161,8 +161,8 @@ mod test {
       ],
     );
     world.do_step();
-    assert_eq!(world.tagged, 0);
-    assert_eq!(world.tagged_by, Some(1));
+    assert_eq!(world.state.tagged, 0);
+    assert_eq!(world.state.tagged_by, Some(1));
   }
 
   #[test]