You will need two browsers and a course containing a forum with ratings turned on. As admin, go to the forum and post. If students don't have them already give students moodle/rating:rate and mod/forum:rate in the course. Leave that screen open and go to your other browser. Log in as student and go to admin's forum post. The rating drop down should appear if you have the capabilities correct. In the student's browser, turn off Javascript and reload the page. You should now have a 'rate' button next to the rating drop down. Alt+tab back to admin and take away one of the two required capabilities. As student, click the rate button. You should get an error. Given them back the capability you removed. Check the student can now submit ratings. Take away the other capability and check that they again get an error.