Take another example of date field.
1. enter the month > 12
2.enter the date > 31, 30,28 or 29 depends on the month end 
date.
3. enter year > or < the client requirement
4. Change the format and check
5. check dd/mm/yy with 0 values
7. check with negative values
8. if u have calendar object next to it, check it shows the 
same date when u r clicking.
9. check are u able to navigate in calendar object, month-
wise, year-wise.
and more.......