White Box Testing

White Box Testing in Software Engineering

White box testing is a method that enables testers to analyze and assess a software system’s internal operations, including its code, infrastructure, and integrations with external systems. An automated build method for a modern Continuous Integration/Continuous Delivery (CI/CD) design process must include white box testing. The terms “white box testing,” “glass box testing,” “structural testing,” “clear box testing,” and “open box testing” are also used to describe this type of testing in software engineering. Focusing on the inputs and outputs through the software and enhancing its security are the main goals of white box testing. 

What Is the Purpose of White Box Testing?

System, integration, and unit testing are all possible during the software development process. Verifying that an application’s working flow is one of white box testing’s fundamental objectives. It is comparing a sequence of specified inputs to desired or expected outputs to identify bugs when a particular input does not provide the desired outcome. Once white box tests are properly executed, they can uncover the following problems and flaws in an application’s code:

Vulnerabilities and Security Gaps : Using white box testing methodologies, it is possible to examine the code and determine whether the application’s development team adhered to the best security practices. Additionally, it examines the code to see whether it is susceptible to recognized vulnerabilities and security breaches.

Anticipated Outcome : In this kind of testing, all probable inputs are applied to certain functions to check if the expected outcome is consistent.

Badly Constructed or Incomplete Routes : White box testing assists in evaluating and determining whether the application’s conditional logic is ineffective, flawed, or unnecessary.

Cycle Testing : This technique checks the effectiveness of single, nested, and concatenated loops. It checks the conditional logic and shows how local and global variables should be handled.

DFT : Data Flow Testing To find variables that have not been initialized properly, it is helpful to keep track of both the variables’ values and where they are as they move through the code. Additionally, it looks for variables that have been erroneously defined or modified but never utilized.

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Various Types of White Box Testing

There are many types of white box testing as follows:

  • Unit testing verifies that each component is functioning as intended by running tests integrated into the application code.
  • Mutation testing is a sort of unit testing that examines the consistency and resilience of the code by designing tests, altering the code in small, haphazard ways, and then rerunning the tests to determine if they still pass.
  • Integration testing is testing the developed code to analyze the points of integration between internal software system components or integrations with external systems
  • Penetration testing involves an ethical hacker posing as an informed insider and trying to attack an application using their in-depth understanding of its environment and code.
  • By using predetermined patterns or machine learning analysis, static code analysis can automatically find flaws or coding problems.
The outline of the white box testing process :
  1. Input: Functional specs, design documentation, source code, and requirements.
  2. Processing: Carrying out risk assessments to direct the whole process.
  3. Proper test plan: Creating test cases that cover the complete code is an example of it
  4. Run: It rinse-repeat until the software is error-free. Additionally, the outcomes are shared.
  5. Output: Final report of the full testing process being prepared as the output.

Popular White Box Testing Techniques

The comprehensive coverage of the source code is one of the key objectives of white box testing. An indicator of code coverage is the percentage of an application’s code that has unit tests confirming its functionality. By utilizing ideas like statement coverage, branch coverage, and path coverage within code coverage, it is feasible to confirm how much of an application’s logic is actually performed and verified by the unit test suite.

Statement Coverage :

A white box testing technique called “statement coverage” makes sure that all of the code’s executable statements are executed and verified at least once. For instance, the test should run each and every range of inputs if a block of code contains multiple conditions, each of which is utilized for a specific set of inputs. This will ensure that all lines of code are actually executed.

Statement coverage assists in identifying unwanted statements, useless branches, lacking statements that are referred to by sections of the code and expired code from previous iterations.

Statement Coverage

Branch Coverage

It is another white box testing technique used to ensure that every branch of conditional logic is covered by unit tests. Branch coverage translates the code into different branches. If there are numerous nested conditional statements, for instance:

if X then..

   if Y then..




      if Z then..




A, C, and D are dependent branches since they only take place when a precondition is met. As it is always performed after A, B is an unconditional branch. The tester uses the branch coverage approach, identifying all unconditional and conditional branches, and creates code to test as many branches as possible.

Branch Coverage

Path Coverage

It is also the popularly used white box testing technique that deals with linear independent paths through the code and it is known as path coverage. A control flow diagram of the program, like the one shown below, will be created by testers.

And test all the separate paths suggests that, in the case of a path from main() to function G, the program should be tested to see if it is accurate along that specific path before proceeding to test any other paths and remedy any flaws.

Path Coverage

Loop Testing

Testing loops is crucial because they are often used and essential to many algorithms. Errors frequently happen at the start and end of loops. Let us look into this white box testing technique here, Simple loops: Test cases are created for easy loops of size n that:

Skip the loop entirely

Only one pass through the loop

2 passes

m passes, where m < n

n-1 and n+1 passes

  • Nested loops : For nested loops, we start from the innermost loop and set all of the loops to their smallest count. The innermost loop is subjected to basic loop tests, and this process is continued until all of the loops have been checked.
  • Concatenated loops : Separate loops that are connected together. For each, simple loop tests are used. Treat them like nesting if they are not self-sufficient.

Condition Coverage

This white box testing technique requires that each distinct condition be covered, as demonstrated in the following case:

READ X, Y IF(X == 0 || Y == 0)


#TC1 – X = 0, Y = 11

#TC2 – X = 1, Y = 0

Multiple Condition Coverage

Using this white box testing technique, each combination of potential conditions and outcomes is examined at least once. Let’s think about the following illustration:


IF(X == 0 || Y == 0)


#TC1: X = 0, Y = 0

#TC2: X = 0, Y = 1

#TC3: X = 11, Y = 0

#TC4: X = 11, Y = 1

How is White Box Testing carried out?

To make understanding white box testing in software engineering easier for you, we’ve broken it down into two simple phases. At the time of evaluating with white box testing, the tester will perform the following sequences.

Step 1: Comprehend the Compiled Code: A tester will frequently study and comprehend the application’s source code as their initial step. The tester must have an extensive understanding of the programming languages used in the apps they are evaluating because white box testing involves testing an application’s internal workings. Additionally, the tester needs to be well-versed in secure coding techniques. Security is frequently one of the key objectives of software testing. The tester should be able to identify security flaws and thwart assaults from hackers and gullible users who might willfully or accidentally introduce malicious code into the application.

Step 2: Create and Execute Test Cases: White box testing’s second fundamental stage entails examining the application’s source code to ensure correct organization and flow. Writing more code to test the source code of the application is one approach. For each procedure in the application—or set of processes—the tester will create a little test. This method, which is frequently carried out by the developer, necessitates that the tester has a thorough understanding of the code.

Example of White Box Testing

Consider the following code:

Printme (int a, int b) {                      

    int result = a+ b; 

    If (result> 0)

     Print (“Positive”, result)


     Print (“Negative”, result)


Verifying all of the decision branches, loops, and statements in the code is the objective of White Box testing in software engineering. White Box test cases would be used to put the statements in the white box testing example above to the test.

A = 1, B = 1

A = -1, B = -3

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Advantages of White Box Testing

  • Code is optimized by white box testing so that hidden errors can be found.
  • White box testing test cases are simple to automate.
  • Due to its coverage of all code paths, this testing is more thorough than other testing methodologies.
  • Even without a GUI, it can be initiated during the SDLC phase.

Disadvantages of White Box Testing

  • Large-scale programming applications require too much time for white box testing.
  • White box testing is more complex and expensive.
  • The developers’ lack of attention to detail may result in production errors.
  • Professional programmers with in-depth knowledge of programming languages and implementation are required for white box testing.

Testing: Black Box vs. White Box

As there are two different ways to test applications: white box testing and black box testing. 
Comparison FactorBlack Box TestingWhite Box Testing
DefinitionA testing strategy is known as “black box testing” involves testing software without being aware of its core architecture. The end-user experience is a major concern here.White box testers are familiar with the program’s internal coding.
GoalThis type of testing’s primary goal is to evaluate the system being tested for functionality.White box testing verifies that the code is of the required quality.
Testing BaseTesting in “black box” scenarios is predicated on external expectations.White box testing provides knowledge of software’s internal programming.
UsageFor higher levels of testing, such as acceptance and system testing, black box testing is fantastic.For lower-level testing, such as integration and unit testing, white box testing is ideal.
Testing MethodTrial and error is the basis of black box testing.White box testing can examine internal boundaries and data domains.
Programming SkillsNo programming expertise is required for black box testing.White box testing calls for considerable programming expertise.
SpeedIt requires less effort and time.It needs a lot of time.
AdvantagesIt works nicely for lengthy code portions.It is beneficial to eliminate any superfluous lines of code that could result in more problems.
LimitationsWith any change to the program, the automated test script needs to be updated.Automated test cases become obsolete if the code is frequently modified.

Popular White Box Testing Tools in Software Engineering

Some of the most widely used white box testing tools are listed below :

  • With the help of Parasoft Jtest, users can maintain development cycles and maintain the quality of their code. Users of its toolset can spot code errors at any level of the software development process.
  • A unit-testing framework for all.net languages is called NUnit. Originally a JUnit port, it has been completely redone with a host of features and compatibility for various.net platforms.
  • HTMLUnit : This GUI-free Java browser models HTML documents and offers an API that enables users to access pages, click links, complete forms, and other functions.
  • PyUnit : This JUnit adaptation for Python includes five essential classes in its unit test module.
  • CppUnit : CppUnit is a unit testing framework that is a C++ port of the popular JUnit framework.


White box testing can be very complicated. The complexity involved greatly depends on the program being tested. While bigger programming applications take days, weeks, or even longer to completely test, a small application that only does a single straightforward function can be white box tested in a matter of minutes. Software applications should undergo white box testing both during development and after each update.