added tets for models - course, assignment, participant, message
added tets for models - course, assignment, participant, message

Cal-CS-61A-Staff/ok,Cal-CS-61A-Staff/ok,Cal-CS-61A-Staff/ok,Cal-CS-61A-Staff/ok,jordonwii/ok,jordonwii/ok,jordonwii/ok,Cal-CS-61A-Staff/ok,jordonwii/ok