Works in Firefox.
In Chrome, you also need:
Note that because we're in the 'scope' of the iframe, $this->one('body') is the body element of the iframe. Clicking on it gives it the focus so that the keys() get to the iframe.
Doesn't work in IE (10 on Win 7, at least). Win 7 can't find the body element (although putting in an echo $this->source()) confirms it's finding the iframe OK.
2. Auto correct
I was putting the text 'i have a comment' into a normal text editor. Turns out IE autocorrects that to 'I have a comment' which means the test fails when it compares the strings after saving.