asciidoctor: ERROR: test.adoc: line 1: only book doctypes can contain level 0 sections

You can encounter the following error:

asciidoctor: ERROR: test.adoc: line 1: only book doctypes can contain level 0 sections

As the error message shows,

you can't contain multiple level 0 sections if the doctype is not book.

Reference:
http://asciidoctor.org/docs/user-manual/#sections