White Box vs. Black Box Testing

April 29, 2021
Amy Patt
Amy Patt

There are two primary kinds of quality assurance (QA) testing; white box and black box. What’s the difference and what value do these opposite, yet complementary, test types bring to the testing environment?

White Box Testing

White box is a software testing technique that checks the internal functions of a system. In this case, the tester has comprehensive knowledge of product’s the internal structure and full access to the source code.

Programming knowledge is necessary to perform white box testing and, in some cases, involves the programmer writing tests for their own code. There are several different methods of testing that fall under this umbrella, including integration testing, coverage testing, regression testing, and unit testing.

Black Box Testing

Black Box testers perform their tests in the opposite fashion of their white box counterparts; they don’t know the inner workings of the product they are testing. When performing black box testing, the internal structure of the software and the source code is hidden.

It might seem like white box testing is a better approach than black box. However, just because black box testers aren’t familiar with the internal side of the software doesn’t mean they’re going in without any information. The customer usually includes a detailed brief of what the product is supposed to do.

The Pros & Cons of Both

When the development process is in the early stages, white box testing can be carried out on small batches of source code to uncover errors. Conveniently, it can be carried out by the internal development team and the systematic method for white box testing can be easily replicated.

However, the preexisting knowledge of product design and development influences white box testers, causing inherent bias that effects the testing outcome. In addition, white box testing can be more time intensive and it can be difficult to find testers with the specialized knowledge required to carry out the tests.

Independent testing carried out by black box testers is necessary for isolating functional errors that might be missed, as well as identifying contradictions or issues with the code that would not be as obvious from a developers’ point of view. Instead of following a predetermined script, black box testers can discover different bugs than the developers would find because they’re performing tests from an end user perspective. For this reason, black box testers don’t need prior programming knowledge or technical skills.

These test cases are easy to create and automate, bringing the value of greater efficiency and unbiased external perspectives into the software development lifecycle (SDLC). Black box testing also tends to keep costs lower since feedback is given earlier in the testing process—and the errors detected can be fixed more easily—making it especially beneficial for testing large systems.

There are drawbacks to black box testing, too. Since each user experience is unique, the test cases conducted by black box testers tend to be high level and less organized. Because the developers and testers have little communication, test paths and processes can be mistakenly duplicated or missed altogether. This lack of communication can also create unclear test specifications. Sometimes testers don’t have enough information to know what to test or they lack the coding knowledge to be able to review certain functions and features accordingly.

When to Use Each Approach

Black box testing makes sense when behavior-testing software and trying to gauge how end users will interact with the product. Black box testing can also be implemented to quickly perform high level tests that check functionality.

White box testing is a longer process and dials into lower levels of the product and code, so the right time to conduct these tests is at the beginning of the SDLC. Interested in trying test IO for free? Sign up for a demo today.

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