Sign Change Coverage
Sign Change Coverage is a structural coverage criterion that requires testing values that cause arithmetic expressions or variables to change sign during execution.
“The coverage of neurons activated with both positive and negative activation values in a neural network for a set of tests.”
(Definition reproduced from the ISTQB Glossary. Copyright belongs to ISTQB.)
View the complete ISTQB GlossaryWhat is Sign Change Coverage?
The objective is to verify that software behaves correctly when numerical values transition between positive, negative, and zero.
Boundary focused: Tests around sign transitions.
Numerical validation: Detects defects in calculations and comparisons.
Structural criterion: Focuses on execution behavior.
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 change 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 change coverage connects tests to the implementation structure where certain defects can hide.
Practice Questions
Question 1
Which statement BEST describes Sign change coverage in the context of ISTQB terminology?
Question 2
A tester needs to explain Sign change coverage to a non‑technical stakeholder. Which approach is MOST appropriate?
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