What is pairwise testing, where is it used, and what does it look like?

Pairwise testing is a test design method where test cases are created to cover all possible pairs of parameter values. The idea is that most errors are caused by the interaction of two factors, so checking all pairs significantly reduces the number of tests compared to exhaustive testing of all combinations.

It is used in testing complex systems with many parameters and options, where full enumeration is impossible due to exponential growth in the number of tests.

Example: if there are three parameters — Color (Red, Blue), Size (Small, Large), Material (Cotton, Wool), then full enumeration would be 2×2×2=8 tests. With pairwise coverage, a smaller number of tests, such as 4, is enough to test all pairs of values.

It looks like a table where each row is a test case covering unique pairs of parameters:

Color	Size	Material
Red	Small	Cotton
Red	Large	Wool
Blue	Small	Wool
Blue	Large	Cotton