added a test for ReVIEW::Book#parts
added a test for ReVIEW::Book#parts

kuad9/review_study,krororo/review,orangain/review,takahashim/review,masawada/review,kmuto/review,krororo/review,kuad9/review_study,kdmsnr/review,masawada/review,suzuki/review,takahashim/review,murashitas/review,murashitas/review,suzuki/review,krororo/review,kmuto/review,kmuto/review,orangain/review