Defect Clusters

Existence of maximum density of bugs in a particular module is called as defect cluster.

An application has four modules to be tested.If the tester finds the percentage of failure in particular module is more ,then a tester reports that a defect clustering has occurred in particular module.
Once the cluster is identified,there is no use of continuing the test process.Instead the build is given back for fixing.

Fatal Error

Fatal error is an error which causes a program to stop processing & abort completly.It returns you to the operating system. During the event the data used by the program is lost. A fatal error occurs typically in any of these cases:

* An illegal instruction has been attempted
* Invalid data or code has been accessed
* The privilege level of an operation is invalid
* A program attempts to divide by zero. (Only for integers; with the IEEE floating point standard, this creates an infinity instead)

In some systems, such as Mac OS X, a fatal error causes the operating system to create a log entry or to save an image (core dump) of the process.