Notification testing in dev server for below 
On Task Assign
ON Task Unassigned
On Task Update 
On Task Delete
On Due date assigne or Change
Subtask Created
On Added Comment
Reminder on Due Date
For Overdue Tasks
For Task Reassigned 
Due Date Extension Approval Request
Due Date Extension Approve
Due Date Extension Reject
Sub task Assignation
Added in Collaboration 
If Team Member try to Mark as Complete without add Time
Task Closure Approval Request
Task Closure Approve
Task Closure Reject
Task Closed
Task Escalation 
Task Priority Change
Task Closure Approver change
Task Deadline Approver change
Attachment added