White Box Testing: What Is It and How Do You Do It?

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Software developers all have the same goal of creating products that are secure, user-friendly, and perform to a high standard. Testing forms a key aspect of any developer’s process, ensuring that the application is up to the right standards and that it functions correctly. White box testing is just one way in which software developers robustly test their creations. Here’s what developers need to know about carrying out white box tests.

What is White Box Testing?

The purpose of white box testing is to examine the internal structure of an application and pinpoint any loopholes in its design. The name arises from the fact that developers look through an application’s outer covering into its inner workings. Some developers refer to this form of structural testing as code-based testing, glass box testing, and transparent box testing. Due to the examination of the internal design of an application, this is the slowest but most comprehensive form of software testing.

The main types of testing include:

  • Unit Testing – Testing of the individual components of the software’s source code. Validates whether each function operates as it should. Identifies defects early throughout the development cycle.
  • Integration Testing – Combining different individual components to see how they perform as a group — designed to uncover defects in how source code interacts with each other.
  • Regression Testing – More tests are carried out to ensure that source code changes have not impacted functionality. Unit and integration tests are reruns as bugs are fixed and new features are added.

These are the main types of structural testing, but there are also other tests developers can run, such as white box penetration testing. This is when the tester is given complete access to the software’s systems and networks and is often used for testing targeted attacks on a specific system.

White Box Testing vs. Black Box Testing

In addition to the types of testing mentioned above, there’s also a form of testing called black box testing. But what’s the difference between black box vs. white box testing? The key difference is that black box testers lack knowledge of the application’s inner workings. Testers are not given an advanced rundown of the target system. If you’re struggling to remember the difference between white box and black box testing, just look at the names. A black box is difficult to see through, whereas you can see everything with a white box.

Developers performing white box vs. black box testing will choose the latter to imitate how the end-user may access and use an application. Both types of testing have their place in the development lifecycle and can provide valuable insight.

White Box Testing Techniques

Code coverage is a key metric used to measure the extensiveness of testing. If only 37% of code was tested, how much confidence would a developer have in their application? Developers use the following formula to calculate code coverage:

Code Coverage = (Number of lines of code executed / Total number of lines of code) * 100

Understanding code coverage enables development teams to assess the quality and efficiency of their testing processes. Obviously, the higher the percentage, the better the test.

Here are the three main testing techniques:

  • Statement Coverage — The most basic form of analysis. Measures the number of statements executed using the same formula as measuring code coverage.
  • Branch Coverage — Measures the number of executed branches within control structures. Again, the same formula is used to calculate branch coverage as code coverage, except the numbers are derived from executed branches and the total number of branches.
  • Function Coverage — Evaluates the number of defined functions. Developers may choose to alter their input parameters to ensure that the functions behave as originally designed. The calculation formula is the same as above.
How to Perform White Box Testing

For software testers, a white box check consists of two basic steps:

  • Step One — Understanding the source code. Testers must be knowledgeable of the internal structure and design of the application they are about to test. They must also know about secure coding practices to guarantee high levels of security.
  • Step Two — Create a test case and execute. Testers may write more code to examine the source code. They may also use various minor tests to analyze each process or group of processes. Most testing involves trial and error and several specialized testing tools.
White Box Testing Example

To better understand how testers approach this process, here’s a white box testing example using a piece of basic sample 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


Software engineers have a simple mission brief when it comes to white box testing. They need to verify every branch, statement, and loop within the code. So, which tests would they run for the above code?

· A = 1, B = 1

· A = -1, B = -3


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