Data flow testing is a family of test strategies based on selecting paths through the program's control flow in order to explore sequences of events related to the status of variables or data objects. Dataflow Testing focuses on the points at which variables receive values and the points at which these values are used.
Data Flow testing helps us to pinpoint any of the following issues:
A variable that is declared but never used within the program.
A variable that is used but never declared.
A variable that is defined multiple times before it is used.
Deallocating a variable before it is used.