White Box Testing: Detailed Overview

In white box testing the internal structure, design, and coding of software are tested for verifying the flow of input-output and improve the design, usability, and security, which is visible for testers and is also known as clear box testing, open box testing, transparent box testing, code-based testing, and glass box testing.

White box testing is one of the two main parts of the box testing approach for software testing. Its equivalent black box testing incorporates testing via an external or end-user type point. On the other hand, white box testing is dependent on applications in working and constitutes internal testing.

The term white box was used because of the see-through box concept. The clear box or white box name signifies the ability to see through the softwares outer shell into its inner workings. Likewise, the black box in black box testing means not seeing the software’s inner workings so that testers can test only the end-user experience.

What do we verify in white box testing?

White box testing incorporates testing of software codes for the following:

  1. Internal security holes
  2. Broken or poorly structured parts in the coding procedure.
  3. The flow of specific inputs by the code.
  4. Expected output
  5. The functionality of conditional loops.
  6. Testing of each statement, object, and function on an individual basis.
white box testing
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The testing could be performed at system, integration, and unit levels of software development. One of the fundamental goals of white-box testing is verifying a working flow for an application. It also incorporates testing a series of predefined inputs against expected or wanted outputs. When particular information does not result in conventional production, we may have encountered a bug.

How do we perform white box testing?

For simplifying the explanation of white box testing, we have divided it into two basic steps. It is done by testers while testing an application using white box testing techniques:

Understanding the source code (STEP 1)

The first thing that a tester will do is learning and understanding the source code of the application. Since white box testing involves testing an application’s inner workings, the test should be knowledgeable in the programming languages used in the applications to be tested. The testing person should be extremely conscious of secure coding practices. Security is frequently one of the primary objectives while testing software. That tester should also find security issues and prevent attacks from hackers and naive users who may insert spiteful code into the application both knowingly or unknowingly.

Creating test cases and execution (STEP 2)

The second essential step for white box testing incorporates testing the application source code for a decent floor and structure. One of the ways is by writing more code for testing the application source code. A tester will develop a little test for each method or series of operations in the application. The tester must have special knowledge of the code, and the developer usually performs this method.

Example of white-box testing

Considering the following piece of code:

Printme (int a, int b) { ———— Printme is a function 

    int result = a+ b; 

    If (result> 0)

     Print (“Positive”, result);


     Print (“Negative”, result);

    } ———– End of the source code 

The main aim of white box testing in software engineering is very fine all the decision branches, loops, and statements in the court. For exercising the statements in the above white box testing example, white box test cases would be:

  • A = 1, B = 1
  • A = -1, B = -3

White Box Testing Techniques

Code coverage analysis is one of the major white box testing techniques. The code coverage analysis eliminates the gaps in a test suitcase. It recognizes areas of a program that are allotted by a set of test cases. Once the holes are identified, we should create test cases for verifying untested parts of the code by increasing the software product’s quality.

There are automated tools available for performing code coverage analysis. Below are a few code coverage analysis techniques white box test could use:

  1. Statement coverage: Every possible statement in the code is required to be tested at least once during the testing procedure of software engineering.
  2. Branch coverage: This technique checks every possible path of a software application.

Apart from the techniques mentioned above, there are numerous coverage types such as condition coverage, multiple condition coverage, path coverage, function coverage, etc.; every method has its advantages and endeavors for testing all parts of a software code. We generally attain 80 to 90% off code coverage by using statement and branch coverage that is considered sufficient.

Below are some of the important white box testing techniques:

  1. Statement coverage
  2. Decision coverage
  3. Branch coverage
  4. Condition coverage
  5. Multiple condition coverage
  6. Finite state machine coverage
  7. Path coverage
  8. Control flow testing
  9. Data flow testing
white box testing

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Types of White Box Testing

Several testing types used for evaluating and applications usability, a block of code a specific software package is incorporated in white-box testing. They are listed below:

Unit testing: It is usually the first type of testing performed on an application. Unit testing is conducted on each unit or block of code as it is developed. The programmer essentially performs unit testing. As a software developer, we can create a few code lines, a single function or an object, and test for making sure that it works before continuing unit testing helps identify most bugs at early stages in the software development life cycle. Bugs identified at this stage as cheaper and easier to fix.

Testing for memory leaks: Memory leaks are the leading principles of slower running applications. A QA professional experienced at detecting memory leaks is necessary to have a slow running software application.

Apart from the above, these are a few testing types that are a part of both BlackBox and white box testing.

Whitebox penetration testing: The tester or developer has full data of the application’s source code, detailed network information, IP addresses involved, and all server information that the application runs on in this testing.

White box mutation testing: Mutation testing is usually used for discovering the best coding techniques for expanding the software solution.

Advantages of White Box Testing

  1. Code optimization by discovering hidden errors. 
  2. Tests can easily automate white box test cases. 
  3. Testing will become more thorough as all code paths are habitually covered.
  4. Testing can start in early SDLC even if GUI is not available.

Disadvantages of White Box Testing

  1. White box testing could be quite difficult and costly. 
  2. White box testing needs professional resources with the most detailed understanding of programming and implementation.
  3. White box testing is time-consuming, and bigger programming applications take the time to test fully.


White box testing could be quite complex, and the environment complexity has a lot to do with the application being tested. A small application that offers a single simple operation could be a white box test in a few minutes. White box testing in software testing should be done with the software application as it is being built after it is written again and again after modifications.