Professors can make tests for students to be used for self-assessment, so they can prepare for exams more successfully, and deepen their knowledge. The results of self-assessment can be seen only by the examinees, and self-assessment tests can be taken unlimited times. 

If you are an examinee in a self-assessment then you have to do the same steps as in an exam except that the self-tests can be found in the "Self-assessment" box.