For this test you will find it easier to have two browsers ie Firefox and Chrome. Create a course containing two assignments. Have a student submit something for both assignments. As a teacher grade the student submissions. Give the a different grade. For example 50 and 70 so that you can see if they are being used in averages. Hide one assignment on the course page. As teacher go to the course gradebook and go to the categories and items page. Click the settings icon for the course itself. Its the cog icon in the actions column. Set aggregation to "mean of grades" if it isn't already. As a teacher or admin go the course gradebook. Go to Settings > Course in the gradebook navigation drop down. Look for the Overview report setting "Hide totals if they contain hidden items" and make sure it is set to "hide". As the student go to your overview report and check that the course total is hidden. It should have been replaced with "-". As teacher, set "Hide totals if they contain hidden items" to "show totals excluding hidden items". As student, refresh the overview report. Check that the course total is equal to the grade for the visible activity. As teacher, set "Hide totals if they contain hidden items" to "show totals including hidden items". As student, refresh the overview report. Check that the course total is equal to the average of the two activity grades.