## Sunday, February 28, 2021

### Data Flow Testing in Software Testing | White Box Testing

This post is on Data Flow Testing. What is data flow testing? Data flow testing in software testing is white box testing. Data flow testing is also a structured testing methodology, based on your program's internal structure. Data flow testing focuses on variables' definition and use. A variable is a memory location that can store a value. A variable's value can be used in a condition or a calculation. Now, in a program, it is possible for the developer to use a variable that doesn't exist or update a variable's value by error. In data flow testing, you examine the variables in your program. View my Data Flow Testing tutorial for more details or read on.

Data flow testing strategies in software testing include:
1) Define Use Testing - DU Testing has some rules and metrics. It tests the paths of the Control Flow Graph (view my Path Testing tutorial to learn about Control Flow Graph) that have a variable defined or used.
2) Program Slices - Program slices strategy divides the program into executable sections, for a variable. You could then test a single program slice independently, for that variable.

Let us see the data flow testing example. This example program computes the Sum of some numbers. Here is the Control Flow Graph when the variable n gets a value of 0 (in Node 4).

If the variable n has a non-zero value, a different path is taken in the Control Flow Graph. The reason is that the while loop is also run. Here is the Control Flow Graph when the variable n gets a value of say, 100, the first time (in Node 4) and 0 the second time (in Node 8).
Let us now learn about Define Use Testing. A particular node in the Control Flow Graph can be either a Define Node or Use Node. A variable is given a value in a Define Node. Examples of Define Nodes are Node 2 (the variable i is given a value), Node 3 (the variable sum is given a value), Node 4 (the variable n is given a value) or Node 8 (again, the variable n is given a value). A variable's value is used in a Use Node. Examples of Use Nodes are Node 6 (the value of variable sum is used; also the value of variable n is used) or Node 7 (the value of variable i is used in the computation) or Node 10 (the value of variable i is used; also the value of variable sum is used in the print statement). Learn about P-use (Predicate Use) and C-use (Computation Use) here. In Define Use Testing, you should identify the Define Use nodes for each variable. I have explained how to find the Define nodes and Use nodes for variables i, n and sum here. In Define Use Testing, you should identify some paths according to your chosen Define Use Testing Metrics and test those paths to find bugs.

Moving on to Program Slices. This data flow testing strategy is useful when your program is large in size. You could identify a program slice (a set of statements) for a single variable, up to any statement in your program. I have explained how to identify program slices for variables i, n and sum here.

Using both Define Use Testing and Program Slices data flow testing techniques, here are four Define Use Paths (pink table below) to test for variable n. In Data Flow Testing, you could test these paths. Similarly, you could identify the paths to test for variable i and variable sum and test them too.

Want to learn Data Flow Testing in detail? Learn Data Flow Testing Metrics? Then please view the complete Data Flow Testing with Example Tutorial. Thank you.