The quality of operation in unexpected states is typically very poor, because there are no common ways to design for the unexpected. Typically, the requirement specifications do not mention the possibility for getting there at all. The designers protect the software from crashing, and provide error messages to the operators, which they can rarely understand. Typically, specification documents do not mention unexpected states specification at all. The design is concerned about preventing system crash, notifying the operators about the exceptional situation. testing cannot be planned for the unexpected. The operators receive a message about something unfamiliar to them, and they can do nothing to cope with the situation.
Updated on 09 Mar 2016.