There are many ways to post an assignment that doesn't actually show up for students: eg, saving it but not publishing it; publishing the assignment but not the module it's in; setting a show by date that is a problem. The calendar (in student view) is currently the only way to see that an assignment is visible to students. However, a) you can only see the calendar in student view by starting from a particular course; 2) multi-section courses show only one section's due dates on the calendar (and don't reveal which section the "test student" is enrolled in). There is no way (other than checking with actual students) to confirm that an assignment is visible to students.
Make a better calendar: one that can show student view for all courses and sections, and one where student view can be "turned on" from the calendar page (vs going back to a course).
