When I "Switched View Mode", I was able to see a duplicate test assignment. Upon deleting the duplicate and "Switching the view mode" back, I was able to see the completed assignment.

Changing to P4. Adding an assignment or volunteering for an assignment should include validation to ensure that a duplicate assignment is not created - unless there is some requirement (doubtful) to have duplicate assignments (in which case there should be a more "Obvious" way to see duplicate assignments).

Thank you for the update. You are right, I know about the bug that one view cannot display duplicates properly. Actually the check would have to consider user, spec, platform and label (if used).

Instead of preventing duplication (who knows, maybe the unlikely usecase will be needed someday...), I'd rather fix the page to show duplicates properly (new row in table in possible some small indication of duplicity)

I agree. I could see where a duplicate assignment might be a valid use case.
Perhaps validation could be as simple as a "Are you sure Y/N", so silly people like me wouldn't assign a duplicate inadvertantly!

I see what I can do but this is a bit of more complex. I'll fix the bug with hidden assignment and add some "duplicate exists" visual annotation to the page so you can quickly see it.

OK, so current status is:
 - test run page (the default view) shows "dupl." labels in case there are duplicate assignments and also the duplicates are now displayed instead of hidden (before)
 - if you creating a volunteer assignment, there is a check for duplicity and if needed, user is asked if he/she really wants to create a duplicate assignment.
 - if tribe leader/manager is creating assignment for someone else, each time he/she presses Add button to add new assignment to the list of assignments to be created, this assignment is validated and if it is duplicate, it is displayed in the table of assignments to be created. So there is only visual warning, not confirmation dialog. 
 - there is one last way to create test assignments for managers, but I didn't implemented any validation for it. It uses completely different UI and logic and this would be very complicated

Changes will be live in 30 minutes. Thank you for reporting.

Thanks Lada, the duplicate validation/notification works well. 

I noticed it alerts you during creation, but if the labels are different, does NOT mark them as a duplicate in the RUN view. I assume this is a feature, and not a bug. Reason: a spec with one label is assigned, and later a spec with a different label is assigned.

Thank you for verification. It is as you said, labels must be also same (or both none) if assignments should be marked as duplicates