Which testing method reduces the number of combinations to all pair combinations?

Orthogonal array testing is a systematic way to reduce the number of test cases while ensuring that all possible pairs of input combinations are covered. This approach uses a mathematical concept to create an "orthogonal array" which allows testers to represent multi-dimensional test cases efficiently. By focusing on all pair combinations, this method ensures that each possible pair of parameter options is tested at least once, while significantly lowering the total number of test cases needed compared to exhaustive testing.

In contrast, boundary value analysis focuses on testing at the boundaries of input ranges rather than input combinations. Exploratory testing emphasizes testers' creativity and experience, allowing them to test the application without predefined cases, which may not ensure pair coverage. State transition testing is used to validate the behavior of a system as it transitions between different states and does not specifically aim to pair all combinations in the way orthogonal array testing does.