I will type randomly what I have in mind. I have only 10 minutes to write all the scenarios I can think off.

Pre-conditions for testing.
1. Check the Wordpress Settings for Comments. This comment should be held for moderation first and should not appear in the post unless it is approved by the admin.
2. Correct values are entered in all the fields ( we can write a very long test case for verifying the validity of the data input made by the users ). For time’s sake, we need to ensure that these 3 fields have the correct error handling code so that it can capture any mistakes made by our users.

Functional :

Success
1. Once comment is submitted, the page should re-refresh then comment is submitted for approval
1. Comment should not appear in the post unless approved
2. If approved, the comment should appear on the correct post
3. If not approved, the comment should not appear anywhere in the post
4. The exact comments submitted by the posted should appear at the correct section of the post
5. Error handling – there should a good feedback for successful submission of the post
… more

Failure
1. Comment appearing immediately on the post
2. Clicking Submit Comment does not submit the comment
3. Clicking Submit crashes the website
4. Error handling needs to be in place. Overflowing the comment field should be handled gracefully.
– more

Performance
1. How long does it take for the comment to be submitted
2. How long does it take for the comment to appear once the admin approved the comment

Load / Concurrency
1. What happens when there are 100 users submitting comments for the same post at the same time

And my 10 minutes if up!!!