Understanding Black Box & White Box Software Testing

Complete testing of a software or mobile app ensures that it serves the purpose it was built for, while meeting all requirements without compromising quality or functionality. For this, testers perform a variety of feasible tests based on pre-determined testing strategies and the availability of resources. The entire software testing process provides an overview of the quality of the software and its risk of failure to end-users and stakeholders.

Among the many types of testing employed, black box and white box testing are typically the most common in almost all software development projects. Let’s explore what it is that both these testing types are for, and their key differences.

Black box testing

Testers perform black box testing when they don’t have any information about how the software works internally. The high level testing technique tests the behavior of the software when it’s subjected to various conditions. The tests are conducted from an end-user or external user’s perspective. Black box testing can be performed on virtually every aspect of software testing including unit and integration testing, system testing, and acceptance testing. It’s also known as box testing or functional testing.

White box testing

White box testing is generally considered as low-level testing. It tests the internal functioning of the software, and is based on coverage of code statements, branches, paths, conditions etc. White box testing is also known as glass box, transparent box, or code base testing. Inputs are chosen to exercise paths through the software’s code to get desired outputs. It’s usually done at the unit level though in some cases, it’s also applied at integration and system levels.

Key differences between the two

Internal & External

Black box testing tests the external behavior of the software while the testers have no knowledge of the internal structure or behavior of the product. Testers who know the internal structure of the product performs white box testing.

Programming & implementation knowledge

Testers performing black box testing need not possess programming knowledge or implementation knowledge to do so. However, to perform white box testing, programming knowledge and implementation knowledge are mandatory.

Automation prospects

Black box testing is considered as an advanced testing technique where programmers and testers need to be involved directly. This makes it challenging to automate black box testing. White box testing, on the other hand, can be automated and is quite easy to do so as well.

Major techniques

Black box testing can generally use one of the three following techniques:

  • Boundary Value Analysis: Focus on testing the input boundaries that are most likely to end up giving erroneous outputs.
  • Equivalence Class Partitioning: Focus on identifying and classifying errors so as to reduce test cases.
  • Error Guessing: Focus on finding defects first and developing corresponding test cases.

When it comes to white box testing, the tester’s knowledge about the system allows him to develop test cases to discover internal defects. The techniques involved include:

  • Statement Tests: Every statement within the code should have a test associated to it, and each statement must be executed in a test cycle.
  • Decision Tests: All decision directions should be executed in a test cycle.
  • Branch Condition Tests: The conditions associated with a specific decision should be tested to see if they are working properly.
  • Data Flow Tests: All variables and data within the system are tested.
  • Multiple Condition Tests: Each point of entry within the code is tested in a test cycle.


Many software development companies tend to not completely perform black box testing especially when there are time constraints. They instead do some quick tests to see if the software’s core features are functional. Some companies perform neither black box nor white box testing but instead implements grey box testing – a combination of black box and white box testing done only at the interface level.

In this age, product quality and usability are more important than ever which demands great effort from testers into ensuring that the end-product was built the right way, with the right functionalities, and without defects.