Personally, I'd say, don't worry about it. As I stated before, 100% coverage may be impossible in some cases, and 90%+ should be acceptable in most cases. That said, in your specific case, you could pass in an invalid url-encoded string.
ClassName myController = new ClassName();
System.assert(false, 'Expected ...
If all the students and contacts are already in salesforce, export them to excel along with their IDs, and in the Related id field in Students, paste the IDs of contacts in ContactId field in student and it will reflect in SF.