White Box Testing: A Complete Guide with Examples and Tools

Software needs to be tested to ensure the quality of the application.  Software testing is the act of building test cases using testing techniques.  Testers use these test cases and techniques to test applications so that software reaches stakeholders without defect.  Moreover, software testing also helps to identify unforeseen errors, use cases or missing requirements.  Testers often test the same code by using different methodologies and tools.   So that you best understand white box testing, First, I’ll define this technique in detail.  Second, I’ll review exactly what is being testing (with examples). Third, I’ll introduce you to some tools used for executing this testing technique.  Finally, I’ll discuss the advantages and disadvantages of white box testing.

what is white box testing?

White box testing is a software testing technique that involves analyzing the application code.  This analysis includes the code architecture, code components, and implementation of each component.  clear box testing, open box testing, structural testing, transparent box testing, code based testing, and glass box testing are other terms for white box testing.  The technique was dubbed ‘white box testing’ because a white box is a transparent box, easily revealing the internal structure of the application to the software tester. 

The tester is able to determine all valid and invalid inputs and outputs by inspecting the code.  Next, the tester can design test cases that measure the actual output against expected output.  Finally, the tester can construct unit and integration tests.  First, let’s take a look at what is being tested.

what is being tested during white box testing?

A software tester should review the code for the following issues:

  • Poorly structured paths in the code.
  • Each statement, object, and function.
  • Flow of inputs and outputs of each function.
  • Security issues introduced by poor coding practice.

After reviewing the code, the software tester can construct test cases. Likewise, once the test cases are complete, they can use them to construct test cases.  Therefore, let’s review the most common examples of this technique.

examples of white box testing

The tester is ready to write tests after reading the code and composing test cases. After that, you can employ some common types of white box tests, including:

transparent components

          • Unit tests – ensure that a single unit of code functions as expected.  They do this by measuring valid/invalid inputs and outputs.  Unit tests can be run anytime code changes.  This allows the tester to verify that a simple unit of function delivers the expected output.  Simply, unit test make sure that code is tested and working in an isolated environment.
          • Integration tests – a combination of units when tested as a group.  These tests ensure integration between apps function as expected.  Furthermore, Integration tests should be run anytime code changes; this allows the tester to verify the integration of units of code.
          • Regression tests – a suite of tests around a feature or set of features.  These tests allow testers to test around a feature or set of features to learn if a small change in one place in the code had an unexpected impact.  Regression tests are created by reusing the unit and integration tests test cases.
          • Penetration tests – tests that attack the code (and network) to expose vulnerabilities of an app.

The tester has reviewed the code and designed test cases.  Moreover, using those test cases, they’ve created tests using the white box tests above.  Now, let’s look at some tools that can help the tester examine the code in it’s static state, as well as help create white box tests.

testing tools

Static code analysis tools are valuable tools to have in any tester’s toolbox.  These tools assist in test automation and finding issues in the code.  Test coverage (by total percent of all lines of code), security vulnerabilities, and code smells are some issues these tools can identify and help remedy.  Here are four good examples of white box testing tools:

We now grasp the methods used to examine the code and write test cases.  We know testers use those test cases to construct tests using some of tools I’ve provided.  Now, let’s discover why white box testing is important and should be used by all software testers.

advantages of white box testing

This testing technique has important assets that will help you discern if this is the right technique for your app.  There are 4 distinct advantages:

  • If there’s an error or bug, then the specific line/s of code that caused the issue can easily be pinpointed, allowing for trace-ability.
  • The tester will know when to stop testing because of the clear boundaries defined within the code.
  • Testing can be performed early in the Software Development Life Cycle (SDLC).
  • Issues found by running unit and integration tests are most often the easiest to fix, thereby reducing costs associated with software development.
  • Testing is easy to automate.  Unit and Integration tests are two Test techniques that are at the bottom of the the practical test pyramid.
Practical Test Pyramid
Mike Cohn’s Practical Test Pyramid

Every testing technique has advantages and disadvantages.  However, for this testing technique, the advantages far outweigh the disadvantages.  Next let’s examine the drawbacks of white box testing.

disadvantages of white box testing

There are four primary drawbacks to using this testing technique:

  • Software testers often don’t have the skills to review code authored by software developers.  Moreover, testers may not have the skill set to write unit or integration tests.
  • The tests are only as good as the author of the tests can make them.  This specifically applies to unit and integration tests.
  • Writing unit and integration tests increases the time it takes to write code.  This means it takes longer to deliver features to customers.
  • Every condition of the app cannot be tested using only this technique.

In other words, this technique requires knowledge that many development teams lack, which is the technique’s biggest drawback.  However, by using white box testing techniques the development team’s skills will grow.  In other words, these professionals must take the time to learn the needed knowledge to use this technique, but it will benefit the team and company over the long term of the project.  Finally, after revealing the advantages and disadvantages, I will show you why you must use the this testing technique.

why use white box testing 

Above all, more than growing the skills of your dev team, the cheapest way to prevent bugs is with white box testing.  White box testing also allows for easier long-term maintenance of the code base.  To fix an issue in code, developers may spend a lot of time debugging code line by line; this is costly in salary and time spent.  However, with more unit and integration tests, developers spend less time debugging.  Above all, since unit and integration tests can be run locally, this allows for these issues to be identified before code is merged into the main line.

In conclusion, you understand what white box testing is, and you understand how to review the code and construct test cases. You’re also aware of the tools needed to constructs these tests, as well as the advantages and disadvantages of this testing technique.  Further, you understand why you must use white box testing.  Now, there’s only one last thing to do – test!

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