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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteWhite-box testing is software testing in which test design is based on the software’s internal structure or processing. Also called structure-based testing, it complements black-box testing, which derives tests from specified behavior without relying on implementation details.
What white-box testing means
NIST describes white-box testing as testing software’s “internal structures or workings.” ISTQB similarly defines white-box, or structure-based, test techniques as those based on analysis of a test object’s internal structure and processing. (NIST CSRC glossary; ISTQB Foundation Level Syllabus)
The defining point is the basis for designing tests: the tester uses knowledge of how the code or system is organized and processed, not just what behavior its specification describes. NIST also lists clear-box, glass-box, transparent-box, and structural testing as related terms.
How it differs from black-box testing
| Aspect | White-box testing | Black-box testing |
|---|---|---|
| Basis for test design | Internal structure and processing of the test object. | Specified behavior, without reference to internal structure. |
| Information used | Knowledge of the implementation or other internal structure being tested. | Behavioral specifications and observable inputs and outputs. |
| What coverage can show | Whether selected structural items, such as statements, decisions, or conditions, were exercised. | Whether selected specified behaviors or scenarios were tested; the exact measure depends on the chosen technique. |
These are complementary test-design approaches, not mutually exclusive types of software or test levels. The same system can be tested against its specified behavior and its internal structure.
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How coverage works
Structural coverage measures whether tests exercise items chosen by a coverage criterion. ISTQB’s glossary includes statement, decision, and condition coverage among code coverage measures. (ISTQB Glossary: Testing Techniques)
- Statement coverage: whether the selected executable statements have been run.
- Decision coverage: whether each outcome of a decision, such as true and false, has been exercised.
- Condition coverage: whether each individual condition within a decision has taken its relevant outcomes.
For example, suppose a function returns one result when an input is above a threshold and another when it is not. A decision-coverage test plan would include inputs that exercise both outcomes. Those tests demonstrate the chosen decision outcomes were reached; they do not prove the function is correct for every possible input or that all requirements have been identified.
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A coverage percentage is meaningful only in relation to its criterion and measured code or structure. Coverage can reveal unexercised items and help guide additional tests, but it is not proof of correctness, requirement completeness, or absence of defects.
Where white-box testing is used
White-box testing is not limited to unit or component tests. ISO/IEC/IEEE 29119-1:2022 notes that structure-based testing can be applied at all test levels, including system testing; its example is measuring menu-item coverage. (ISO/IEC/IEEE 29119-1:2022)
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The method applies wherever an internal structure can inform test design. The particular coverage items depend on the test object and the chosen technique.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What white-box testing is not
White-box testing is not simply another name for static analysis. White-box describes a basis for designing tests around internal structure; static analysis examines software artifacts without executing them. Nor does the term require a particular programming language or guarantee that tests will find defects.
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