As an aside to the discussion at hand, what papers/books/online articles are good to read to learn about how to come up with good properties and generators?
On Wed, Apr 30, 2014 at 3:36 PM, Alex Miller <a...@puredanger.com> wrote: > The only hard parts about property based testing are the properties and the > generators. ;) > > On Wednesday, April 30, 2014 6:38:19 AM UTC-5, henry w wrote: >> >> Hi, I wanted to get started with clojure.test.check (formerly >> simple-check) and I am new to property based testing. >> >> I plucked clojure.core/group-by for no particular reason as a function to >> test. >> >> I started by stating some properties i think should hold: >> >> ;; 1. applying the grouping key function to each member in a grouping >> should result in the grouping key >> ;; 2. flattening the vals of the group-by result should give back the >> contents of the original collection. >> ;; 3. no element appears in more than one grouping. > > > those seem good > >> >> >> so far so good I think. there may be others but this seems ok for now. >> >> now, how to generate some data. >> >> for group-by we need two params: >> 1) a grouping function >> 2) a collection of items to be grouped >> >> If I start by naively generating collections of maps (containing keyword >> keys and int vals, for example), the data is of the right shape to use in >> group by, but there is no guarantee that: >> 1) any of the maps share a key that I could use for grouping >> 2) the values under a common key are shared >> >> This is really the crux of my problem.... ideally I would have the >> generator *mostly* produce data which is actually doing to result in the >> sort of collection i might want to call group-by on in real life (ie not >> have everything grouped under nil on each generation). So should i create a >> generator that creates keywords (which i will want to use as grouping >> function) then have another generator that produces what are going to be the >> values under this grouping key, then a generator that uses both of these to >> create collections of maps from these. then i would have to find out what >> the grouping keyword was that was generated.... this could all work, I have >> read enough about generators to have a stab at this... but is it the right >> approach? > > > You don't seem to be leveraging the possibilities of the grouping function. > If you create a grouping function that maps many random values into a small > number of groups, then everything may get easier. Some candidate functions: > first character of the keyword, length of the keyword, etc. > > Or working backwards is often useful with a generator - generate the > grouping values first, then use the inverse of the grouping function to > generate data that maps to that group and populate the input with that. > >> >> >> as far as implementing tests for the properties so far, I have done >> property 2 above, using a basic generator and yanking out an arbitrary key >> from it.... clearly a flawed approach as not much 'realistic' grouping is >> going to happen here. >> >> (def vector-of-maps (gen/such-that not-empty (gen/vector (gen/such-that >> not-empty (gen/map gen/keyword gen/int))))) >> >> (def all-elements-are-grouped >> (prop/for-all [group-by-input vector-of-maps] >> (let [a-map-key (-> group-by-input first keys first)] ;; >> hmm, seems far from ideal >> (= (set group-by-input) (-> (group-by a-map-key >> group-by-input) vals flatten set))))) >> >> help appreciated... perhaps I need to learn more about the paradigm first, >> but resources linked from the readme are all a bit more basic than this. so >> if you know of some more advanced tutorials please let me know. >> >> Thanks > > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with your > first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en > --- > You received this message because you are subscribed to the Google Groups > "Clojure" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to clojure+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
