MarkUsProject/Markus — pull request #1842 by kubasub (2014-10-18 16:29:05+00:00)
Title: Added Assignment model, rspec tests

rspec tests added:
- when an assignment is past due date
- for `Assignment#criterion_class`
- some more Assignment attribute validations

I modified `Assignment#criterion_class` to make the following test pass:
```
Assignment
#criterion_class
when the marking_scheme_type is nil
returns nil
```