One approach you can use is write the generators in such a way that they generate the final answer group-by should return, then you write code which does the inverse to group by and then you check the group by answer is equal to the originally generated solution.
On Wednesday, April 30, 2014 11:38:19 PM UTC+12, 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. > > 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? > > 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.
