A bit of cleanup and refinement before refactoring.

tests/map.cpp

@@ -22,6 +22,8 @@ TEST_CASE("dijkstra algo test", "[map]") {
         test["walls"],
         test["limit"]);
 
+    REQUIRE(map.INVARIANT());
+
     map.make_paths();
     Matrix &paths = map.paths();
 
@@ -31,6 +33,7 @@ TEST_CASE("dijkstra algo test", "[map]") {
       dump_map("RESULT", paths);
     }
 
+    REQUIRE(map.INVARIANT());
     REQUIRE(paths == expected);
   }
 }