RE: test from JS

Yes sure here what I used for this little test using steem-js (https://github.com/steemit/steem-js/tree/master/doc#broadcast-api)

const result = await steem.broadcast.commentAsync(postingKey, '', '', username, permlink, title, body, JSON.stringify({tag:['test'], format: 'markdown'}));

or without the async / await

const result = steem.broadcast.comment(postingKey, '', '', username, permlink, title, body, JSON.stringify({tag:['test'], format: 'markdown'}), function(err, result){ // Do something });