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
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