What is the primary technique used to validate all possible pairs of input in black-box testing?

The primary technique used to validate all possible pairs of input in black-box testing is pairwise testing. This method is highly effective because it focuses on testing combinations of input parameters, specifically validating all possible pairs. Given that input combinations can grow exponentially with the number of parameters, pairwise testing adopts a systematic approach to ensure that all pairs of input values are tested, significantly reducing the number of test cases required while still maintaining coverage of potential interactions.

This technique is particularly useful in scenarios where exhaustive testing is impractical due to the large input space, and it helps identify defects rooted in the interaction of parameter pairs, which are commonly responsible for failures in software applications. By applying pairwise testing, test analysts can achieve a robust level of confidence in the software's functionality while optimizing their resources.

In contrast, other techniques such as orthogonal array testing, exploratory testing, and state transition testing, while they serve specific purposes in test design and execution, do not focus specifically on the pairwise interaction of input values. Orthogonal array testing is more about achieving a balanced representation of all parameters, exploratory testing emphasizes discovering defects through unscripted exploration, and state transition testing is centered on validating state changes in the system rather than input pairs.