The errors of concern here are not programming or design errors, but behavior that may occur and must be handled appropriately. Like a file open request because of a non existing file. Therefore these errors are at least runtime errors.
For a system, which behavior emerges as a result of its function and its interaction with an unpredictable environment, the Pareto principle holds for the distribution of its main functions and its error handling across its behavior. Typically about 10%-20% of the events that signal an error, result in 90%-80% of the behavior associated with error handling. While 90%-80% of the events that relate to the main functions of the system typically result in 10%-20% percent of the overall behavior which is unrelated to error handling.
Error handling is most often a matter of redirecting the handling to the party in charge to allow them to attempt recovery by retrying, continue with reduced or gracefully degraded function, by failing safely altogether, or continue as normal treating the error as a warning.
Dezyne is very effective in allowing engineers to discover the emergent error behaviors–i.e., without having to resolve to devising test scenarios, writing test code and running tests—as well as designing the handling of the respective error conditions.