Unit verification effects on reused components in sequential project releases

Background. The effects of different practices on fault distributions in evolving complex software systems is not fully understood. Software reuse and unit verification are prac- tices used to improve system reliability by minimising the number of late faults. Reused software benefits from already being verified while unit verification aims to find faults early.Aims. We want to study effects of software reuse and unit verification on future modifications, fault densities of software units, and fault distributions.Method. We applied statistical analysis to a sample of 520 units that were reused and modified within four sequential projects from one product line in the telecommunication domain.Results. In reused units, the results of unit verification are correlated to a smaller degree of modifications and decreased fault densities.Conclusion. Unit verification in complex systems may improve system evolution in terms of smaller modifications and decrease of fault densities. The unit verification faults in reused components may be used as predictors of component modification and fault density