Japanese language ability test（日本語検定）

In last June, the Japanese language ability test was held for the first time.
This test was not developed for those who learn Japanese as the second language, but
for native Japanese!

Accroding to webpage, the purpose of this test is...

日本語検定は、小学生から社会人まで、それぞれの生活環境と発達段階に応じて取り組むことができます。自分自身の日本語をとらえなおし、日本語を正しく使えるようにするための一つの手立てとなること、それが願いです。
(brief translation: Japanese language ability test is made for every Japanese, from elementary school children to business person). Everybody can have a chance to check their own usage of Japanese language. This may be a tool for correcting their daily use of wrong ways of speaking Japanese.)

questions are from six aspects of Japanese language, that is, respective expression(KEIGO), grammar, vocaburary, word knowledge, knowledge of kanji, and orthography.

There are six levels, though the top level test was not held in June.

I am wondering whether this kind of knowledge test correlates to another types of language
ability, general reading comprehension or verbal IQ.

of course, it does not mean that examinee cannot speak Japanese even if they failed to pass this test...