I recently had to get some coverage metrics for an assignment. I struggled for a long time with finding the right buttons in Intellij Idea. Then at some point I found "run 'project' with Coverage" in the menu. Push this and you will see coverage metrics when it is done running. Below is an image of where this is in the menu:
If this does nothing you may have to configure this. Go to "Edit Configurations..." as seen above. This will open a menu like below. Here you can configure the code coverage settings.
If the "run with code coverage" is successful you will se the metrics like below. Where you can see if you missed any methods, lines or whole classes!
I hope this helps someone out there :) Let me know if it did down in the comments below!