Black-Box vs. White-Box Testing

The software testing field’s lexicon is huge and continues to grow. Newcomers to the field may be intimidated by the thought of learning so much jargon. Luckily, we’ve written a post to make this situation at least a little bit less daunting by covering the old “black box vs. white box testing” dilemma.

By the end of the post, you’ll know the definitions, strengths, and weaknesses of both forms of testing. Let’s dive in.

Black Box vs. White Box: It’s About Visibility

In our context, “black” and “white” mean “opaque” and “transparent,” respectively. So, black box testing refers to forms of software testing in which the internals of Black box vs white box visibility

the application are hidden from the tester. White box testing is the opposite: the test knows and cares about the internal details of the application.

White box and black box testing aren’t types of testing in the way that unit testing and load testing are. Rather, they’re categories or labels we apply to the many different forms of testing so we can have interesting conversations about their properties.

White Box Testing in More Depth: Advantages, Disadvantages, and Examples

We’ll now walk you through some of the main pros and cons of white box testing. You’ll also see some types of software testing that usually fall under the white-box umbrella.

Advantages of White Box Testing

  • Localized feedback. White box tests, such as unit tests, usually provide precise feedback. In other words, when the test fails, you know exactly where the problem is, making fixing the problem easy.
  • Simplicity and speed. White box tests tend to be simpler to write and usually don’t require an involved preparation phase. Also, they’re often very fast because they don’t rely on complicated and slow dependencies.
  • Can sidestep the UI. The UI is often the most volatile layer of an application. It can change a lot, causing tests that rely on it to fail frequently. So, white box tests that bypass the interface and talk directly to the inner layers of the application can be more stable than other tests.

Disadvantages of White Box Testing

  • It can lead to fragile tests. White box tests can be fragile if they’re too coupled with low-level details of the system’s structure.
  • Fewer people can perform it. White box testing requires knowledge of the system’s internal structure, and that often requires coding skills. So, the pool of potential people who can work with this kind of testing is smaller.
  • Less realistic. White box testing, while able to detect design problems and bugs, often can’t detect unmet requirements. In other words, you can ensure you’re building the thing right, but not necessarily whether you’re building the right thing.

Examples of White Box Testing automation testing

  • Unit testing
  • Integration testing
  • Code review
  • Mutation testing
  • Control-flow testing

Black Box Testing in the Spotlight: Pros, Cons, and Examples

After evaluating white box testing, let’s do the same to its counterpart.

Advantages of Black Box Testing

  • Larger potential pool of testers, since it doesn’t require knowledge of the system’s internals, nor coding skills.
  • More realistic. Black box testing methods usually test applications in a way that more closely resembles a real interaction with a user, thus detecting issues that other forms of testing can’t.
  • Requirement validation. Black box tests (e.g., end-to-end testing or acceptance testing) can validate whether the application works as the user expects it.

Disadvantages of Black Box Testing

  • Less precise feedback. When things go wrong in black box testing, there’s often a larger surface area for you to find and fix the problem.
  • Complexity and slowness. Black box testing usually requires a more elaborate setup. And automated black box tests are generally slower to run than their white box counterparts.

Examples of Black Box Testing

  • End-to-end testing
  • UI testing
  • Acceptance testing

Black Box vs. White Box Testing: Does This Distinction Still Matter?

You’ve just learned about black box and white box testing and have seen the definition, the pros, the cons, and some examples of each one. But now we must ask: is this distinction still relevant?

Well, somewhat. This categorization allows for some interesting conversations. For instance, it makes it easier to know who performs the testing and whether the tests are fragile or robust. On the other hand, recent evolutions in the software development process have rendered the categorization less relevant, blurring the lines between the two labels. Kent Beck, for instance, states that TDD renders the white box vs. black box dichotomy irrelevant.

Where should you go from here? Now that you know a bit more about software testing and how you can categorize its different types, you might want to brush up on your unit testing skills. Or you might be interested in learning more about test automation in general. Either way, the answer is the same: education is always the next right step. Thanks for reading!

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Carlos Schults
Carlos Schults
Carlos is a consultant and software engineer with experience in desktop, web, and mobile development. Though his primary language is C#, he has experience with a number of languages and platforms. His main interests include automated testing, version control, and code quality.