Allow negative score for rubric and change default grade calculation method

BEFORE UPGRADE create an assignment with rubric grading method, create rubric without 0-points levels grade some students using rubrics review students grades in gradebook, they should be calculated using this unintuitive method backup assignment and save backup file for later upgrade open existing assignment, make sure the first option in the rubric (about locking 0-points) is not checked mark another student in this assignment make sure the grade calculation is the same as before create a new assignment with rubric grading, edit rubric make sure the 0-points is locked by default add the same criteria/levels as before grade students the same way as before check the grades in the gradebook, they should be calculated as: score / maxscore x maxgrade (where score is the total number of points in selected levels in the rubric; maxscore is the sum of maximum points for each criterion; maxgrade is whatever you set up in the module grade settings, usually 100) restore the assignment from the backup created before upgrade make sure the 0-points option is not checked there try editing the rubric without changing this option and make sure the option remains unchecked Regrading: Create an assignment with any rubric Grade some students As student make sure you can see rubric As teacher edit the rubric and change the flag "lock zero points" Make sure grades-have-changed confirmation is displayed Confirm As student make sure you can see grade but not rubric As a teacher open student grading again, it should be preserved, save grade As student make sure you can see grade and rubric (grade may have changed) Negative scores: Create an assignment with a rubric where some levels have negative number of points Grade students, some with positive and some with negative final scores Make sure the grade in the gradebook is max(0, score / maxscore x maxgrade) Changes to behat test: To ensure that the behavior did not change (despite the change in the behat test), do the following: Overwrite edit_rubric.feature with the version from upstream At line 32 add: | When converting rubric score to points/scale assume that minimum number of points is 0 | | Run this test and make sure it passes