Description of problem: student can accidently hit enter key, and test gets submitted. perhaps we even need a second page... are you really ready to finish test? by the way, you havne't answered questions 2 or 8 yet...
in my browser, at least, no matter where your focus is the return key submits the test. the "are you sure" page would probably be the only reasonable solution to the problem. not sure whether a javascript popup might even be a good way to handle this...
now, for lessons or tests, if you submit the whole page (either via return or the button at the bottom) there is a javascript check that you answered all questions, and if not, an option to cancel the submission (and go to the first missing question). this specifically should not happen if the user submits and individual question. since this is javascript, YMMV per browser, but the worst that is likely to happen is that the check doesn't work and the user is no worse off than before (the kind of javascript i like). if something goes wrong and actually somehow probihits them from submitting, they can turn off javascript. this development is currently on webtest.