coding_18843_add_comment

 - [x] code functions
    - [x] post_comment (controller)
    - [x] create_comment (model)
 - [ ] code unit test
    - [ ] test_post_comment_ok (controller)
    - [ ] test_post_comment_notok (controller)
    - [ ] test_post_comment_ok (model)
    - [ ] test_post_comment_notok (model)

You means post_create_comment()?