LEARN. PRACTICE. GROW.Concept and mechanism
Data-test design starts by dividing the input space according to relevant rules. For authorization requiring an integer amount in cents x greater than 250000, the boundary is open: in domain-testing terminology, ON is 250001, the nearest representable point inside the region, and OFF is 250000, the excluded boundary itself. For x greater than or equal to 250000, the boundary is closed: ON is 250000 and OFF is 249999. Precision belongs to the model; without the smallest unit, nearest may be undefined. When two conditions delimit the region, vary one boundary while keeping the other condition satisfied so the test has a clear interpretation.
Guided application
In a service with channel, currency, and customer type, testing each value once does not ensure that relevant interactions were exercised. A pairwise selection covers value pairs while respecting feasible-combination constraints. It may miss a failure requiring all three factors together. Choose interaction strength according to risk and add combinations known to be critical. Random generation also needs a domain and an oracle. A generator configured only for positive amounts will never investigate rejection of negative values. With tools such as Hypothesis, choosing a domain does not mean distribution is uniform or resembles real traffic. Retain counterexamples and add directed cases for important boundaries.
For integer cents x>250000: ON 250001, OFF 250000.
Common pitfalls
Omitted precision; pairs treated as exhaustive; domain without invalid inputs.
Related topics: Analysis and evidence in the test process · Priority and residual risk · States, CRUD, and journeys
Define partitions, boundaries, and interactions before generating data.
Reference: NIST combinatorial testing FAQ · CTAL-TA v4.0 (2025)