getStandardMenuLink example

$this->assertSession()->statusCodeEquals(403);

    // Delete menu links.     foreach ($this->items as $item) {
      $this->deleteMenuLink($item);
    }

    // Delete custom menu.     $this->deleteCustomMenu();

    // Modify and reset a standard menu link.     $instance = $this->getStandardMenuLink();
    $old_weight = $instance->getWeight();
    // Edit the static menu link.     $edit = [];
    $edit['weight'] = 10;
    $id = $instance->getPluginId();
    $this->drupalGet("admin/structure/menu/link/{$id}/edit");
    $this->submitForm($edit, 'Save');
    $this->assertSession()->statusCodeEquals(200);
    $this->assertSession()->pageTextContains('The menu link has been saved.');
    $menu_link_manager->resetDefinitions();