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Software Testing / Chapter 04 01 / 06

White-Box
Test Techniques.

Statement testing · Branch testing

Based on an analysis of the test object's internal structure.

◉ ISTQB FOUNDATION · SECTION 4.3

The focus · two code-related techniques 02 / 06

Because of their popularity and simplicity

The entire software implementation is taken into account.

There are more rigorous white-box test techniques used in safety-critical, mission-critical, or high-integrity environments. There are also techniques used in higher test levels, such as API testing. These are not discussed in this syllabus.

Technique 01

S

Statement Testing.

Coverage items are executable statements. The aim is to exercise statements in the code until an acceptable level of coverage is achieved.

Technique 02

B

Branch Testing.

Coverage items are branches. The aim is to exercise branches (transfers of control) in the code until an acceptable level of coverage is achieved.

4.3.1 · Statement Testing 03 / 06

Exercising executable statements

Each statement with a defect will be executed.

When 100% statement coverage is achieved, all executable statements in the code have been exercised at least once. This may cause a failure demonstrating the presence of the defect.

However, exercising a statement will not detect defects in all cases. It may not detect data-dependent defects, and it does not ensure that all decision logic has been tested.

◉Covers all executable statements100%

✗May miss data-dependent defectsGAP

✗May not exercise all branchesGAP

Formula

Exercised/ TOTAL

4.3.2 · Branch Testing 04 / 06

Transfers of control

Conditional and unconditional branches.

A branch is a transfer of control between two nodes in the control flow graph. Conditional branches typically correspond to a true or false outcome from an "if...then" decision, a switch/case outcome, or a decision to exit or continue in a loop.

Exercising a branch will not detect defects in all cases — for example, defects requiring the execution of a specific path in code.

→if...then decisionsCONDITIONAL

→switch/case outcomesCONDITIONAL

→Loop continue/exitCONDITIONAL

→Straight-line codeUNCONDITIONAL

Branch coverage subsumes statement coverage. 100% branch coverage also achieves 100% statement coverage — but not vice versa.

4.3.3 · The Value of White-box Testing 05 / 06

Fundamental Strength

Entire
implementation
accounted for.

Facilitates defect detection even when the software specification is vague, outdated, or incomplete. The code itself is the source of truth.

&

Corresponding Weakness

Defects
of omission.

If the software does not implement one or more requirements, white-box testing may not detect the resulting missing functionality.

Performing only black-box testing does not provide a measure of actual code coverage. White-box coverage measures provide an objective measurement of coverage.

Conclusion · structure-based techniques 06 / 06

Objective measurement of coverage

Necessary information to increase confidence.

— TECHNIQUE / 01

Statement

— TECHNIQUE / 02

Branch

— APPLICATION

Static & Dynamic

White-box techniques can also be used in static testing — well suited to reviewing code not yet ready for execution, pseudocode, and other high-level logic which can be modeled with a control flow graph.

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