Sign-sign Coverage
Sign-Sign Coverage is a structural testing criterion that verifies combinations of sign changes across related variables or expressions during execution.
“The coverage achieved if by changing the sign of each neuron it can be shown to individually cause one neuron in the next layer to change sign while all other neurons in the next layer do not change sign for a set of tests.”
(Definition reproduced from the ISTQB Glossary. Copyright belongs to ISTQB.)
View the complete ISTQB GlossaryWhat is Sign-sign Coverage?
It helps identify defects caused by interactions between multiple positive, negative, or zero values in computational logic.
Combination testing: Evaluates multiple sign relationships.
Interaction focus: Detects defects involving related variables.
Numerical analysis: Useful for mathematical software.
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. Sign-sign 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 Sign-sign coverage connects tests to the implementation structure where certain defects can hide.
Practice Questions
Question 1
Which statement BEST describes Sign-sign coverage in the context of ISTQB terminology?
Question 2
A tester needs to explain Sign-sign coverage to a non‑technical stakeholder. Which approach is MOST appropriate?
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