Software developers frequently encounter failures that occur only as the result of an interaction between two components. Failure triggering fault interactionsTesters often use pairwise testing – all pairs of parameter values – to detect such interactions. Combinatorial testing beyond pairwise is rarely used because good algorithms for higher strength combinations (e.g., 4-way or more) have not been available, but empirical evidence shows that some errors are triggered only by the interaction of three, four, or more parameters (see graph). These results have important implications for testing. If all faults in a system can be triggered by a combination of n or fewer parameters, then testing all n-way combinations of parameters can provide high confidence that nearly all faults have been discovered. We are producing methods and tools to generate tests for all n-way combinations of parameter values, using improved combinatorial testing algorithms for constructing covering arrays, and automated generation of test oracles using model checking.