valid data such as customer name but is too long for you to store

using no data or blank or default data

using invalid data such as negative values

illegal data such as numbers in an alphanumeric field

response time - whether an application responds quickly enough .

using valid data but including problematic expressions such as O'Toole as a family name.

using valid data

whether the application will run in different environments, eg. mobile devices and desk tops.

security of the site, can it it be hacked