Introduction to Combinatorial Testing : Chapman & Hall/CRC : 9781466552296 : 1466552298 : 31 Jul 2013 : "Software testing has always faced a seemingly intractable problem: for real-world programs, the number of possible input combinations can exceed the number of atoms in the universe, so as a practical matter it is impossible to show through testing that the program works correctly for all inputs. Combinatorial testing offers a (partial) solution. Empirical data show that the number of variables involved in failures is small. Most failures are triggered by only one or two inputs, and the number of variables interacting tails off rapidly, a relationship called the interaction rule. Therefore if we test input combinations for even small numbers of variables, we can provide very strong testing at low cost. As always, there is no "silver bullet" answer to theproblem of software assurance, but combinatorial testing has grown rapidly because it works in the real world"--