How to Perform White Box Testing – Explained with a Simple Example

Understanding White Box Testing with a Simple Example

In my career so far, I have seen the testers to be the most enthusiastic community in the software industry.

The reason being, that tester always have something in their scope to learn. Be it domain, process or technology, a tester can have a holistic development if they wish to.

But as they say “There is always a dark side”. Testers also avoid one type of testing which they feel is very complicated and developer’s piece of cake. Yes, you have guessed it right. It’s the “WHITE BOX TESTING”.

How to perform white box testing

White box and black box testing:

If we go by definition, “White box testing” (also known as clear, glass box or structural testing) is a testing technique which evaluates the code and internal structure of the program.

It’s the counterpart of Black box testing.

In simple words – In Black box testing, we test the software from a user’s point of view, but in White box, we see and test the actual code. In a Black box, we do testing without seeing the internal system code, but in a White box we do see and test the internal code.

White box testing technique is used by both developers as well as testers. It helps them understand which line of code is actually executed and which is not. This may indicate that there is either missing logic or a typo, which eventually can lead to some negative consequences.

Steps to perform White box testing:

Step #1 – Understand the functionality of the application through its source code. Having said that, it simply means that the tester must be well versed with the programming language and other tools and techniques used to develop the software.

Step #2– Create the tests and execute them.

When we discuss testing, “coverage” is the most important factor. Here I will explain how to have maximum coverage in the context of White box testing.

Also read => Cause and Effect Graph – Dynamic Test Case Writing Technique For Maximum Coverage

Types of white box testing:

There are different types and different methods for each white box testing type. See below image. (click on image to enlarge)

White box testing types

Today, we are going to focus mainly on the execution testing types of ‘Unit testing white box technique’.

The three main White box testing Techniques are:

  1. Statement Coverage
  2. Branch Coverage
  3. Path Coverage

Let’s understand these techniques one by one with a simple example.

#1 Statement coverage

In the programming language, a statement is nothing but the line of code or instruction for the computer to understand and act accordingly. A statement becomes an executable statement when it gets compiled and converted into the object code and performs the action when the program is in running mode.

Hence “Statement Coverage”, as the name suggests, is the method of validating that each and every line of code is executed at least once.

#2 Branch Coverage

“Branch” in a programming language is like the “IF statements”. If a statement has two branches: true and false.

So in Branch coverage (also called Decision coverage), we validate that each branch is executed at least once.

In case of an “IF statement”, there will be two test conditions:

  • One to validate the true branch and
  • Other to validate the false branch

Hence, in theory, Branch Coverage is a testing method which when executed ensures that each branch from each decision point is executed.

#3 Path Coverage

Path coverage tests all the paths of the program. This is a comprehensive technique which ensures that all the paths of the program are traversed at least once. Path Coverage is even more powerful that Branch coverage. This technique is useful for testing the complex programs.

Let’s take a simple example to understand all these white box testing techniques.

White box testing example

Consider below simple pseudocode:


 INPUT A & B
C = A + B
IF C>100
PRINT “IT’S DONE” 

For Statement Coverage – we would need only one test case to check all the lines of code.

That means:

If I consider TestCase_01 to be (A=40 and B=70), then all the lines of code will be executed

Now the question arises:

Is that sufficient?

What if I consider my Test case as A=33 and B=45?

Because Statement coverage will only cover the true side, for the pseudo code, only one test case would NOT be sufficient to test it. As a tester, we have to consider the negative cases as well.

Hence for maximum coverage, we need to consider Branch Coverage, which will evaluate the “FALSE” conditions.

In the real world, you may add appropriate statements when the condition fails.

So now the pseudocode becomes:

 INPUT A & B
C = A + B
IF C>100
PRINT “IT’S DONE”
ELSE
PRINT “IT’S PENDING” 

Since Statement coverage is not sufficient to test the entire pseudo code, we would require Branch coverage to ensure maximum coverage.

So for Branch coverage, we would require two test cases to complete testing of this pseudo code.

TestCase_01: A=33, B=45

TestCase_02: A=25, B=30

With this, we can see that each and every line of code is executed at least once.

Here are the conclusions so far:

  • Branch Coverage ensures more coverage than Statement coverage
  • Branch coverage is more powerful than Statement coverage,
  • 100% Branch coverage itself means 100% statement coverage,
  • 100 % statement coverage does not guarantee 100% branch coverage

Now let’s move on to the Path Coverage:

As said earlier, Path coverage is used to test the complex code snippets, which basically involves loop statements or combination of loops and decision statements.

Consider this pseudocode:

 INPUT A & B
C = A + B
IF C>100
PRINT “IT’S DONE”
END IF
IF A>50
PRINT “IT’S PENDING”
END IF 

Now to ensure maximum coverage, we would require 4 test cases.

How?

Simply – there are 2 decision statements, so for each decision statement, we would need to branches to test. One for true and other for the false condition. So for 2 decision statements, we would require 2 test cases to test the true side and 2 test cases to test the false side, which makes a total of 4 test cases.

To simplify these let’s consider below flowchart of the pseudo code we have:

Path coverage 1

So, In order to have the full coverage, we would need following test cases:

TestCase_01: A=50, B=60

TestCase_02: A=55, B=40

TestCase_03: A=40, B=65

TestCase_04: A=30, B=30

So the path covered will be:

Path coverage 2

Red Line – TestCase_01 = (A=50, B=60)

Blue Line = TestCase_02 = (A=55, B=40)

Orange Line = TestCase_03 = (A=40, B=65)

Green Line = TestCase_04 = (A=30, B=30)

See also => Different Types of testing

Conclusion

Note that the statement, branch or path coverage does not identify any bug or defect that needs to be fixed. It only identifies those lines of code which are either never executed or remains untouched. Based on this further testing can be focused on.

Relying only on black box testing is not sufficient for maximum test coverage. We need to have combination of both black box and white box testing techniques to cover maximum defects.

If done properly, White box testing will certainly contribute to the software quality. It’s also good for testers to participate in this testing as it can provide the most “unbiased” opinion about the code. :)

About the author: This is a guest article by Shilpa C. Roy. She is working in software testing field for the past 9 years in domains like Internet advertising, Investment Banking and Telecom. She has also cleared the CTAL test manager exam with good score.

This is just a start and there is much that can be discussed about this topic. Let us know if you have any questions about the methods we discussed in this article. Feel free to suggest more simple or advanced techniques/tools that you are using for doing white box testing.




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43 comments ↓

#1 vismay

Hello Sir,
I am vismay.
I am working as a QA Engineer in company and have 3 years of experience in manual testing and 6 month experience in automation.
I want to start freelancing please give me suggestions regarding this, how can i start and prerequisites?

#2 Nikolay

Good article. A very thorough discussion with nice examples.

#3 komal

hi
the example shared is very simple and easy to understand clearing all concepts.

thnak you

#4 Ranjan

Very nice.
In the Branch Coverage, the example is incorrect. Psl correct.

TestCase_01: A=33, B=45

TestCase_02: A=25, B=30

In this case, it allways goes to else part, never executed first part.

#5 Kunjal Gandhi

Good one.. Today I get cleared of concept behind 100% branch and statement coverage

#6 Sumit

can you provide white box testing tools?

#7 Chetan Metker

hello shilpa mem & Vijay sir:This is a good article about
how to perform WBT.actually most of the people follow the BBT because they have not proper knowledge about coding,tools or frameworks etc.but in thie time in market WBT is most important technique to find a defect in software application or product.
I hope this article gives a new direction to think about WBT.
Thanks for this article…!!

#8 gourav

Can you please explain Path coverage in more details?

#9 hritik

can you provide flex testing tools,please note down here

#10 Anand Awate

In the Branch Coverage, the example is incorrect. Psl correct.

TestCase_01: A=33, B=45

TestCase_02: A=25, B=30

In this case, it allways goes to else part, never executed first part.

#11 Andy

A clearer example of when full path should be used would be helpful. Full path can be extremely time consuming, and so long as full decision and statement coverage has been achieved, it might also be unnecessary. Typically full path is reserved for safety or critical systems.

#12 Kelis

A really good answer, full of raotntaliiy!

#13 Teerna

I read so many stuffs on White Box testing but didn’t understand until I read this article. Thanks! Thorough and easy to understand!

#14 D.Selvakumar

How i can learn this, conducting any course this in Chennai or through online.

#15 nithhya

hi mam nd sir ,ur articleis good nd in my opinion video explanation vil b dam good than this plz upload video explanation
thank u

#16 P Prasanti lata

I am a beginner in testing , really very nice aricle

#17 P Prasanti lata

Can any one please explain the completely the difference between condition coverage & path coverage or they are same?

#18 etaert

efteg

#19 Ganesh Wagh

Good article very helpful

#20 karthick kumar

very nice to understand! thank u

#21 Leela

Wow …much useful with clear explanation .. Tank u sooo muchhh

#22 Raza Ali

Its, really greate explanation

#23 GEETHA

GOOD

#24 reva

give me some example for testing

#25 Swapnesh

Nice

#26 shilpa fate

very nice explaination with example.

#27 Anantha

Wonderful ! I never thought it could be explained so nice and in such way that it is easy to understand.

#28 ishan

Good article very helpful and
very nice explaination with example.

#29 Ms K.

Very Good Explanation. Many thanks for posting it. I am currently preparing for CTFL . Please suggest me any good reads as my exam is due in 2 and half weeks time. I am an ICT teacher want to switch in software testing.

#30 ssp

give some s/w development eg….

#31 Yasmin

I can’t understand with full path coverage concept, can u please anyone can explain.

#32 hiral

hii
i have 1 year experience in manual teasting. i shift in pune so please suggestion me how to got a job in pune??

#33 reshma

This is very good artical.

#34 ramya

can i have about white box testing and its types with any simple C language code as an example and how the code is analysed in each test

#35 llDUMBASSll

help me how to use whitebox pm in my email t.y

#36 rohit shingade

Hi vismay i am rohit plzz send your details we provide online trainings for our students all over the globe if our client needs such technology we wilp contact you.
Rohit Shingade
Training Director
StarTech online Training

#37 Allen Urban

It’s an interesting article, but GenRocket has an automated platform and process that does white box testing, fully tests and cuts the time and cost of testng way down.

#38 Manzur

Thanks for the nicely organized article.

I have a confusion about the ‘path coverage’. Test case 1 and Test Case 3 (in fact Test case 2 as well) is a repetitive test for the TRUE side of decision statement 2. Here the total independent path is identified 4. But if we apply the cyclomatic complexity metric here, the total number of independent path would be 3; which reduces the requirement of 1 test case.

#39 Nuwangi

Nicely explained. Very clear, Thanks

#40 Aleksandar Ereman

where can i read about operations testing or all if the unit testing

#41 dipak

I sir mam. I have just complete software testing course and i want a job . atleast i want experience salary does’nt matter.

#42 Yevhenii

Can you please help and draw flowchart for this task.

1. Pick up and read the newspaper.
2. Look at what is on television.
3. If there is a program that you are interested in watching then switch the television on and watch the program.
4. Otherwise.
5. Continue reading the newspaper.
6. If there is a crossword in the newspaper then try and complete the crossword.

A. SC = 1 and DC = 3.
B. SC = 1 and DC = 2.
C. SC = 2 and DC = 3.
D. SC = 2 and DC = 2.
E. SC = 1 and DC = 1.

#43 Chris

Thank you finally got it <3

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