A program fails. Under which circumstances does the failure occur? Starting with a single failure-inducing input (“The input ((4)) fails”) and an input grammar, the DDSET algorithm uses systematic tests to automatically generalize the input to an abstract failure inducing input that contains both (concrete) terminal symbols and (abstract) nonterminal symbols from the grammar—for instance, “((<expr>))”, which represents any expression <expr> in double parentheses. Such an abstract failure inducing input can be used
Note: As of now, we check each abstraction independently of others, and then merge them which necessitates isolation later. An alternative route is to simply accumulate abstractions as your find them, and when generating, regenerate each abstract node that you have accumulated. With this, we can be sure that each node that we mark as abstract is truly abstract. A problem here is that of semantic validity. That is, if say the first abstraction has only 0.5 chance of producing a valid input, and the next abstraction candidate has again only 0.5 chance of producing a valid input, combining them together will reduce the probability of valid input in any generation to 0.25, and as abstractions accumulate, the probability of generating semantically valid inputs drop. Hence, we instead identify them independently and later merge them, with the trade off being a later isolation step.
Another difference is that during isolation we leave every possibly causative part intact. That is, if A or B is necessary for fault reproduction, we leave both A and B as concrete. A user may instead change it to leave either A or B as concrete.
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ACM Distinguished Paper