White Box Testing: A Complete Guide with Techniques, Examples, & Tools

What is White Box Testing?

White box testing, also known as clear, glass box, or structural testing, is a testing technique that involves evaluating the code and internal structure of a program.

White box testing focuses on examining the code structure and ensuring that the internal operations align with the specified requirements. It also aims to thoroughly test all internal components. 

My Experience

Having worked in the software testing field for almost a decade, I have noticed that testers are the most enthusiastic professionals in the software industry.

Their enthusiasm stems from the constant learning opportunities they have. Testers always have something new to learn, whether it’s a domain, a process, or a technology. They can develop a comprehensive skillset if they choose to.

However, there is always a darker side to every profession. Testers often tend to avoid white box testing because they perceive it to be complicated and something that primarily falls under the domain of developers.

Coverage

White Box Testing focuses on the following coverage areas:

1. Code coverage: Evaluate the coverage of the code.

2. Segment coverage: Ensure that each code statement is executed at least once.

3. Branch Coverage or Node Testing: Cover each code branch in all possible ways.

4. Compound Condition Coverage: Test each condition with multiple paths and combinations to reach that condition.

5. Basis Path Testing: Test each independent path in the code.

6. Data Flow Testing (DFT): Track specific variables through each possible calculation to identify dependencies and verify their correct use.

7. Path Testing: Define and cover all possible paths through the code.

8. Loop Testing: Test single loops, concatenated loops, and nested loops to ensure proper functionality.

Reasons for Performing WBT

White Box Testing is performed to:

• Ensure that all independent paths within a module are tested.
• Verify the correctness of logical decisions.
• Test the boundaries and operational bounds of loops and internal data structures.

White Box Testing helps in discovering the following types of bugs:

• Logical errors that occur when designing and implementing functions, conditions, or controls that deviate from the program’s requirements.
• Design errors resulting from discrepancies between the logical flow of the program and its actual implementation.
• Typographical errors and syntax checking issues.

Programming Skills Required

To perform White Box Testing effectively, testers need to write test cases that cover the complete program logic.

This requires a thorough understanding of the program, including its specification and code. Testers need to have knowledge of programming languages and logic to perform this type of testing.

Limitations

It is not feasible to test every path of loops in a large program. Exhaustive testing is impractical in such cases.

However, this doesn’t mean that White Box Testing is not effective. By selecting important logical paths and data structures for testing, it is possible to achieve practical and effective testing.

Difference Between White-Box and Black-Box Testing

Simply put, Black Box Testing focuses on testing the software from a user’s perspective, while White Box Testing involves inspecting and testing the actual code.

In Black Box Testing, the internal system code is not visible, whereas in White Box Testing, the internal code is visible and can be tested.

White Box Testing is used by both developers and testers to understand which lines of code are executed and which are not. It helps identify missing logic or typos that may have negative consequences.

Recommended read => A complete guide to Black Box testing

Steps to Perform WBT

Step #1: Understand the functionality of the application through its source code. Testers need to be well-versed in the programming language and other tools and techniques used in software development.

Step #2: Create and execute tests.

When it comes to testing, “coverage” is crucial. Maximizing coverage is a key aspect of White Box Testing. Here, I will explain how to achieve maximum coverage with respect to White Box Testing.

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

Types and Techniques of White Box Testing

Various types and techniques make up the field of White Box Testing.

Refer to the image below for a visual representation:

In this article, we will mainly focus on the execution testing types of the ‘Unit testing white box technique’.

3 Main White Box Testing Techniques:

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

It is important to note that statement, branch, or path coverage alone does not identify bugs or defects that need to be fixed. They simply identify lines of code that have not been executed or have not been touched. Further testing can then be focused on those areas.

Let’s understand each of these techniques with a simple example.

#1) Statement Coverage:

A statement in programming refers to a line of code or instruction that the computer executes. An executable statement is a statement that compiles into object code and performs an action when the program is running.

“Statement Coverage” involves validating whether each line of code has been executed at least once.

#2) Branch Coverage:

A branch in programming, such as an IF statement, can have two branches: true and false.

In Branch Coverage (also known as Decision Coverage), the objective is to validate whether each branch has been executed at least once.

For an IF statement, this requires testing both the true and false branches separately.

#3) Path Coverage

Path Coverage involves testing all possible paths through a program. This technique ensures that every path is traversed at least once. Path Coverage is even more powerful than Branch Coverage and is particularly useful for testing complex programs.

Let’s take a simple example to illustrate these White Box Testing techniques.

Also check => Different Types of testing

White Box Testing Example

Consider the following simple pseudocode:

INPUT A & B
C = A + B
IF C>100
PRINT "ITS DONE"

For Statement Coverage, only one test case is needed to cover all the lines of code.

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

Now, let’s consider the following:

1. Is that sufficient?
2. What if we consider TestCase_02 as A=33 and B=45?

Statement Coverage alone is not sufficient to test the entire pseudo code. We need to consider negative cases as well.

For maximum coverage, we need to consider “Branch Coverage”“. Branch Coverage ensures that both the true and false conditions are tested.

So, with the updated pseudo code considering Branch Coverage, we would require two test cases:

TestCase_01: A=40, B=70

TestCase_02: A=33, B=45

By using these test cases, we can ensure that each line of code is executed at least once.

Here are the conclusions we can draw:

• Branch Coverage ensures more coverage compared to Statement Coverage.
• Branch Coverage is more powerful than Statement Coverage.
• 100% Branch Coverage implies 100% Statement Coverage.
• However, 100% Statement Coverage does not guarantee 100% Branch Coverage.

Now let’s move on to Path Coverage:

As mentioned earlier, Path Coverage is used to test complex code snippets that involve loops or combinations of loops and decision statements.

Consider the following pseudocode as an example:

INPUT A & B
C = A + B
IF C>100
PRINT "ITS DONE"

END IF
IF A>50
PRINT "ITS PENDING"
END IF

To achieve maximum coverage, we would require four test cases.

Why? There are two decision statements, so for each decision statement, we would need two branches to test (one for the true condition and one for the false condition). That makes a total of four test cases.

Let’s simplify this by considering the following flowchart:

To achieve full coverage, we need the 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

The covered paths are:

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)

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White Box Testing Tools

Here is a list of top white box testing tools:

#1) Veracode

Veracode’s white box testing tools help identify and resolve software flaws quickly and cost-effectively. It supports multiple programming languages and enables testing of desktop, web, and mobile applications. For more information, visit the Veracode website.

#2) EclEmma

EclEmma is a free Java code coverage tool originally designed for test runs and analysis within the Eclipse workbench. To install or learn more about EclEmma, visit their website.

#3) RCUNIT 

RCUNIT is a testing framework for testing C programs. It is free to use under the terms of the MIT License. For more information and download instructions, visit the RCUNIT website.

#4) cfix

cfix is a unit testing framework for C/C++ that aims to make test suite development as simple and easy as possible. It is specialized for use in NT Kernel mode and Win32. Visit the cfix website for installation instructions and more details.

#5) Googletest 

Googletest is Google’s C++ test framework. It supports test discovery, death tests, value-parameterized tests, fatal and non-fatal failures, XML test report generation, and more. Visit the Googletest website to download and learn more about this tool.

#6) EMMA

EMMA is an easy-to-use, free Java code coverage tool with various features. For more information and to download EMMA, visit the EMMA website.

#7) NUnit

NUnit is an open-source unit testing framework for .NET languages. It supports data-driven tests and parallel test execution, among other features. NUnit 3 is released under the MIT license. Visit the NUnit website for downloads and more information.

#8) CppUnit

CppUnit is a C++ unit testing framework and a port of JUnit. It supports test output in XML or text format and allows the creation of unit tests with their own class. CppUnit is licensed under LGPL. To download and learn more about CppUnit, visit their website.

#9) JUnit

JUnit is a simple unit testing framework for Java that supports test automation and Test Driven Development. It is licensed under the Eclipse Public License. Visit the JUnit website for downloads and more details.

#10) JsUnit

JsUnit is an open-source unit testing framework and a port of JUnit for client-side JavaScript testing. It is licensed under GNU Public License 2.0, GNU Lesser Public License 2.1, and Mozilla Public License 1.1. Visit the JsUnit website for downloads and more information.

Also, check all the tools we have listed under Static code analysis here.

Feel free to suggest any other simple or advanced tools that you use for white box testing.

Conclusion

Relying solely on black box testing is not sufficient for achieving maximum test coverage. A combination of both black box and white box testing techniques is needed to effectively cover all potential defects.

When performed properly, White Box Testing significantly contributes to the overall software quality. Testers’ involvement in this type of testing provides an objective perspective about the code and helps identify any potential issues. 🙂

If you have any questions about the methods discussed in this article, please let us know.