drupal hook_menu incorrect affect menu_rebuild - where see the log

When I try to create view, and also something else, the menu could not be rebuilt well, and can not access the view page... at all.
After long time effort, found out that my module did not do well on hook_menu, and I fix it. All work well again. When creating view, create record in menu_router well...

So if something wrong in hook_menu, it will affect the menu_rebuild and make all menu_router related things not working. But there is no error log information about this.

If something incorrect in hook_menu, where could I get some information about it?

The following is correct hook_menu.
function test_menu() {
  $items['testpage'] = array(
    'page callback' => 'testpage',
    'access arguments' => array('access content'),
    'type' => MENU_CALLBACK,
    );
  return $items;
}

function testpage() {
  return 'This is a test page';
}