Property-based testing with Clojure test.check Reid Draper @reiddraper 

(= a b ) 

(= [5 2 1] (reverse [1 2 5])) (= [1 2 3 4 5] (reverse [5 4 3 2 1])) (= [5] (reverse [5])) (= [] (reverse [])) 

(= [5 2 1] (reverse [1 2 5])) (= [1 2 3 4 5] (reverse [5 4 3 2 1])) (= [5] (reverse [5])) (= [] (reverse [])) (= [7 8 2 5] (reverse [5 2 8 7])) (= [55 54 53] (reverse [53 54 55])) (= [-15 15] (reverse [15 -15])) (= [true false] (reverse [false true])) 

(def reverse-property (prop/for-all [a (gen/vector gen/int)] (reversed? a (reverse a)))) 

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Property-based testing is a powerful testing technique, embodied by Clojure test.check. 

example-based testing property-based testing test.check 

example-based testing property-based testing test.check 

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0 ‘() [] {} Integer/MAX_VALUE false -1 

Our tests are only as mischievous as our imagination 

{:3aBA "~e", ({"" false} \") ("r" "" {{} 0, :y {0 \+}}), [2 {} [[] {0 :v7}]] -1/4, (1 2 \') {}, :4 ["" ({0 true})], {false {}, {(0) (\^)} 0, ("m" [false]) ((true) {}), [[\t] ()] {}} -3} 

(= a b ) 

A change in perspective is worth 80 IQ points. - Alan Kay 

example-based testing property-based testing test.check 

generative testing random testing 

never forgets edge-cases 

thousands of tests 

encodes a function’s invariants directly 

(concat a b) ;; Returns a lazy seq representing the concatenation of the elements in the supplied colls. 

(prop/for-all [a (gen/vector gen/any) b (gen/vector gen/any)] (= (count (concat a b)) (+ (count a) (count b)))) 

(prop/for-all [a (gen/vector gen/any) b (gen/vector gen/any)] (= (count (concat a b)) (+ (count a) (count b)))) universal-quantification 

(prop/for-all [a (gen/vector gen/any) b (gen/vector gen/any)] (= (count (concat a b)) (+ (count a) (count b)))) binding 

(prop/for-all [a (gen/vector gen/any) b (gen/vector gen/any)] (= (count (concat a b)) (+ (count a) (count b)))) property 

(tc/quick-check 100 my-property) ;; => {:result true, ;; :num-tests 100, ;; :seed 1395110930836} 

thinking in properties 

roundtrip trusted-implementation input/output relation 

roundtrip 

(prop/for-all [a gen/any-printable] (= a (-> a prn-str edn/read-string))) serialize de-serialize 

trusted-implementation 

(def transient-property (prop/for-all [a (gen/vector gen-action)] (= (apply-actions #{} a) (apply-actions #{} (filter-transients a))))) 

input/output relation 

(prop/for-all [a (gen/vector gen/any) b (gen/vector gen/any)] (= (count (concat a b)) (+ (count a) (count b)))) 

example-based testing property-based testing test.check 

github.com/clojure/ test.check 

clojure clojurescript pedestal core.matrix collection-check byte-streams 

quickcheck Haskell (QuickCheck) 2000 Erlang (EQC) 2006 Scala (ScalaCheck) ~2008 

let's see an example 

(-> #{} (conj 109) (conj -110) transient (disj! -110) persistent! (conj -110)) 

(-> #{} (conj 109) (conj -110) transient (disj! -110) persistent! (conj -110)) 

(def transient-property (prop/for-all [a (gen/vector gen-action)] (= (apply-actions #{} a) (apply-actions #{} (filter-transients a))))) 

(tc/quick-check 1e5 ;; 100,000 transient-property) 

{:result false, :failing-size 92, :num-tests 2893, :fail "...", :shrunk {:total-nodes-visited 440 :depth 83 :result false :smallest "..."}} 

[[:conj 109] [:conj -110] [:transient ] [:disj -110] [:persistent!] [:conj -110]] 

[[:disj -108] [:disj -24] [:disj 89] [:transient] [:conj 12] [:disj -136] [:transient] [:conj -145] [:conj -8] [:persistent!] [:persistent!] [:conj 25] [:conj 142] [:conj 146] [:persistent!] [:transient] [:conj 95] [:persistent!] [:disj -86] [:transient] [:persistent!] [:transient] [:persistent!] [:conj -109] [:transient] [:transient] [:persistent!] [:disj -6] [:transient] [:persistent!] [:conj -50] [:persistent!] [:conj -166] [:transient] [:conj 136] [:persistent!] [:persistent!] [:transient] [:disj 155] [:persistent!] [:transient] [:transient] [:disj 143] [:persistent!] [:persistent!] [:transient] [:conj -10] [:transient] [:conj -59] [:conj -34] [:transient] [:transient] [:disj 111] [:transient] [:disj -33] [:transient] [:conj -96] [:transient] [:disj 93] [:disj -130] [:conj 88] [:disj 14] [:transient] [:disj 9] [:persistent!] [:disj 86] [:conj 109] [:conj -45] [:persistent!] [:persistent!] [:disj -141] [:conj -14] [:persistent!] [:persistent!] [:conj -104] [:conj -83] [:persistent!] [:persistent!] [:conj -73] [:conj 13] [:persistent!] [:persistent!] [:persistent!] [:disj -14] [:conj -129] [:disj -53] [:transient] [:conj -110] [:conj 60] [:conj 11] [:disj -128] [:disj -42] [:disj 18] [:disj 73] [:disj 33] [:transient] [:persistent!] [:persistent!] [:transient] [:persistent!] [:transient] [:disj -123] [:disj -141] [:conj -26] [:conj -92] [:conj -116] [:conj 101] [:disj -133] [:conj 58] [:transient] [:disj -110] [:persistent!] [:disj 105] [:conj 26] [:conj -110] [:persistent!] [:transient] [:persistent!] [:persistent!] [:disj -5] [:conj 117] [:transient] [:persistent!] [:disj 96] [:persistent!] [:disj 52] [:persistent!] [:disj -132] [:transient] [:transient] [:conj -108] [:disj 121] [:persistent!]] 

[[:conj 109] [:conj -110] [:transient ] [:disj -110] [:persistent!] [:conj -110]] 

CLJ-1285 

fixed in clojure 1.6 

github.com/reiddraper/ clojure-transient-test 

generators 

(prop/for-all [a (gen/vector gen/any) b (gen/vector gen/any)] (= (count (concat a b)) (+ (count a) (count b)))) generators 

any any-printable boolean byte bytes char char- alpha-numeric char-ascii hash-map int keyword list map nat neg-int pos-int ratio s-neg-int s-pos- int string string-alpha-numeric string-ascii tuple vector 

(gen/sample gen/boolean) (false false false false false true false false true true) boolean 

(gen/sample gen/int) (0 0 -2 -3 1 3 -2 0 0 -9) int 

(gen/sample (gen/vector gen/int)) ([] [1] [2 0] [1 2 -1] [] [0] [-4] [] [-8] [4 0 2 -8 -9]) vector 

(last (gen/sample gen/any-printable)) {:3aBA "~e", ({"" false} \") ("r" "" {{} 0, :y {0 \+}}), [2 {} [[] {0 :v7}]] -1/4, (1 2 \') {}, :4 ["" ({0 true})], {false {}, {(0) (\^)} 0, ("m" [false]) ((true) {}), [[\t] ()] {}} -3} any 

bind choose elements frequency no-shrink not- empty resize return sample sample-seq shrink-2 sized such-that 

(gen/sample (gen/return :foo)) (:foo :foo :foo :foo :foo :foo :foo :foo :foo :foo) return 

(gen/sample (gen/choose 5 10)) (7 8 9 6 6 5 8 9 10 10) choose 

(gen/sample (gen/elements [:clojure :haskell :erlang :python :ruby])) (:clojure :haskell :haskell :clojure :clojure :python :cloj ure :clojure :ruby :ruby) elements 

(gen/sample (gen/one-of [gen/boolean gen/byte])) (119 true -24 120 -93 true false 27 false false) one-of 

(gen/sample (gen/frequency [[5 (gen/return :weekday)] [2 (gen/return :weekend)]])) (:weekday :weekday :weekend :weekday :weekday :weekend :wee kend :weekend :weekday :weekday) frequency 

(gen/sample (gen/such-that #(not= 0 %) gen/int)) (-1 -2 -1 2 3 -5 -6 6 -5 -1) such-that 

(gen/sample (gen/fmap odd? gen/int)) (false true false true true false false false false false) fmap 

(gen/sample (gen/fmap odd? gen/int)) (false true false true true false false false false false) apply odd? to every generated value 

(gen/sample (gen/bind (gen/not-empty (gen/vector gen/int)) #(gen/tuple (gen/return %) (gen/elements %)))) bind 

([[0] 0] [[1 -2] 1] [[2 2] 2] [[-3 -3] -3] [[4 -4] -4] [[2 1] 2] [[-6 -6 -5 -1] -5] [[8 -5 6 -6 -6 -5 7 -7] 8] [[-3 2 -5 -4] -5] [[7 5] 5]) tuples of vector and chosen element 

example-based testing property-based testing test.check 

[org.clojure/test.check "0.6.1"] 

A change in perspective is worth 80 IQ points. - Alan Kay 

github.com/clojure/ test.check github.com/reiddraper/ clojure-transient-test