How to set the comment body field to be required?
For What ever content type you are giving comments options, you need to go to 

structure &gt;&gt; Content types &gt;&gt; Edit the particular content type &gt;&gt; there will be comments fields tab &gt;&gt; over there  will be list of comments field, in that    comment_body(machine name) wil be required by default. 

If not, make it required by editing that field.