4 Data Flow Testing
In data flow-based testing, the control flowgraph is annotated with information about how the
program variables are defined and used. Different criteria exercise with varying degrees of
precision how a value assigned to a variable is used along different control flow paths. A
reference notation is a definition-use pair, which is a triple of (d, u, V) such that V is a
variable, d is a note in which V is defined, and us is a node in which V is used. There exists
a path between d and u in which the definition of V in d is used in u