This is a common problem with data generators (whether test.check or any
other generator I know of). In general the problem of "giving me random
(but not ridiculous) data that will also effectively act as a test" is
hard. test.check has a number of controls that can be applied; spec exposes
some of those, provides some other controls (like :gen-max in coll-of etc),
and allows the ability to override generators either in the spec definition
or at later points via either name or path. There is a tension between spec
conciseness and generator robustness and finding the right balance is a bit
of an art.
If you could share a bit more about how you are testing this, it might
suggest some other options. Are you generating data with gen/generate or
gen/sample, using clojure.spec.test/test, or something else?
On Monday, July 4, 2016 at 1:19:22 PM UTC-5, Sebastian Oberhoff wrote:
>
> I set myself the exercise of converting k-SAT CNF-formulas to 3-SAT
> formulas, a task that most theoretical computer scientists will be familiar
> with. For that purpose I defined the spec
>
>
> (s/def ::literal (s/or :symbol symbol? :negated-symbol (s/spec (s/cat :not
> #{'not}
> :symbol symbol?))))
>
> (s/def ::disjunction (s/spec (s/cat :or #{'or} :literals (s/+
> ::literal))))
>
> (s/def ::cnf-expression (s/spec (s/cat :and #{'and} :disjunctions (s/+
> ::disjunction))))
>
> Examples for this would be
> '(and (or a b c d) (or e f))
>
> '(and (or a b c) (or d) (or e f g h i j))
>
> So basically an AND of ORs. However after running some generative tests my
> computer began getting really hot. The problem here isn't that I am trying
> to solve an NP-complete problem. I am only testing the reduction. I don't
> care at this point whether any of these formulas are actually satisfiable.
> The problem turned out to be that test.check was generating absurdly large
> CNF-formulas from this spec. I'm talking symbol names ~1000 characters long
> and the overall formula containing ~1000 symbols.
> I could probably mend this problem by overwriting the appropriate
> generators. But seeing how this is the very first spec I'm using for
> generative testing and I'm already running into this after just 3 lines of
> specs, I can easily imagine that I'd end up peppering every spec I'll ever
> write with custom generators saying "this list should only contain 50
> elements", "this string should not contain emoji's" etc... And even that
> might not suffice once I begin composing specs into larger hierarchies
> since the size of the test cases would grow exponentially in the number of
> layers of abstraction.
> Is there a more workable solution for this problem?
>
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