node test: Stub out first element of search box.

frontend_tests/node_tests/search.js

@@ -337,6 +337,8 @@ run_test("initiate_search", () => {
         is_searchbox_text_selected = true;
     });
 
+    $("#search_query")[0] = "stub";
+
     search.initiate_search();
     assert(typeahead_forced_open);
     assert(is_searchbox_text_selected);