Filter codes of method_decorators on coverage
Add test for ContentDocument::XHTML#read
Add test for ContentDocument::XHTML#title
Add test for ContentDocument::XHTMl#title of content with empty title
Fix test name
Add tests for Manifest::Item#xhtml?
Add a test about Itemref equality
Fix Itemref#linear? to return true or false
Add test for Itemref#== for the time when not equal
Add tests for EPUB#each_page_on_spine
Add tests for Metadata::Meta s
Add tests about inspect