Counterexample
A counterexample is a concrete instance that demonstrates a stated property, rule, formula, or universal claim does not hold.
BDD in Action, Second Edition
A counterexample is a concrete case showing where a proposed rule or expected behavior does not apply or produces an incorrect result.
- How it is used
- Uses concrete exceptions during requirements conversations to challenge assumptions and define acceptance criteria.
- How deep it goes
- Explains counterexamples through questioning, tables, rule clarification, and automated acceptance criteria.
- Examples
- Uses ineligible flights, outdated dates, nonqualifying flight numbers, cancellations, and future bookings as concrete counterexamples.
- What you can do after
- Apply it via structured conversations and examples to clarify rules and produce precise acceptance tests.
Read how BDD in Action, Second Edition explains counterexample →
Learn Haskell by Example
A counterexample is an input that causes a tested property to fail, demonstrating that the property does not hold universally.
- How it is used
- Uses failing generated inputs to test properties and guide debugging.
- How deep it goes
- Defines failure and explains deterministic shrinking down to a minimal falsifying input, including the Arbitrary shrink function.
- Examples
- Uses a failing rot13 symmetry test, an alphabet-rotation test, and shrink results for characters and associative maps.
- What you can do after
- Diagnose property or implementation bugs with smaller, repeatable failing inputs.
Related concepts
- shrinkingaddressed by · Shrinking is a test-case minimization technique that reduces a failing input while preserving the failure.
- scenarioused by · A scenario is a concrete description of a situation or conditions, often including actions and expected or possible outcomes, for analysis or evaluation.
- acceptance criteriaproduces · Acceptance criteria are verifiable conditions that a requirement, feature, or deliverable must satisfy to be considered acceptable or complete.
- Example Mappingused by · Example Mapping is a collaborative technique that organizes user stories, rules, examples, and questions to clarify requirements and expected behavior.
- scenario keywordcontrasts with · Scenario, also called Example, is a Gherkin keyword that introduces an executable example of expected behavior in a feature file.
- property-based testingproduced by · Property-based testing is a software-testing technique that generates varied inputs and checks whether specified general properties of the software’s behavior hold across them.
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