Decision Coverage
Decision coverage is a white-box coverage metric that measures whether every decision outcome in the code has been executed during testing.
“The coverage of decision outcomes.”
(Definition reproduced from the ISTQB Glossary. Copyright belongs to ISTQB.)
View the complete ISTQB GlossaryWhat is Decision Coverage?
Decision coverage ensures that each decision, such as an if statement, has evaluated to both true and false at least once.
Decision outcomes: Every branch created by a decision should be executed.
Coverage measurement: Helps identify untested logic paths.
Relationship to branch coverage: Decision coverage is often equivalent to branch coverage for simple decisions.
Real World Example
A tax calculation module applies different deductions depending on income band, residency status, and submitted documents.
Reviewing the final tax amount is not enough when important code paths may never execute during testing. Decision coverage helps the tester reason about the structure behind the result.
The tester works with the developer to identify decisions or paths in the calculation logic and designs inputs that exercise the meaningful alternatives.
The team gains better evidence about hidden logic because Decision coverage connects tests to the implementation structure where certain defects can hide.
Practice Questions
Question 1
Which statement BEST describes Decision coverage in the context of ISTQB terminology?
Question 2
A tester needs to explain Decision coverage to a non‑technical stakeholder. Which approach is MOST appropriate?
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