A utility library for test.check



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test.chuck is a utility library for test.check.

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Please note that as of version 0.2.0, test.chuck (mostly) supports ClojureScript, and requires a minimum Clojure version of 1.7.0. Using ClojureScript requires a minimum test.check version of 0.8.0.

Leiningen dependency coordinates:

[com.gfredericks/test.chuck "0.2.7"]


General Helpers

(require '[com.gfredericks.test.chuck :as chuck])


A helper function for being able to scale your test run count with an environment variable. To use with defspec, simply wrap your test-count argument in a call to times:

(defspec foo-bar-test (chuck/times 20)

This will normally run the test 20 times, but if you set the TEST_CHECK_FACTOR environment variable to e.g. 3.5, it will run the tests 70 times.


(require '[com.gfredericks.test.chuck.generators :as gen'])

There are a few minor generators and helpers, see the docstrings for details:

  • for (described below)
  • string-from-regex (described below)
  • subsequence (for subsets and similar)
  • cap-size
  • partition
  • map->hash-map
  • sub-map
  • bounded-int
  • double


A macro that uses the syntax of clojure.core/for to provide the functionality of gen/bind, gen/fmap, gen/such-that, and gen/tuple:

(gen'/for [len gen/nat
           bools (gen/vector gen/boolean len)]
  [len bools])

(gen/sample *1)
;; => ([0 []]
;;     [0 []]
;;     [2 [false true]]
;;     [3 [true false true]]
;;     [1 [true]]
;;     [5 [true true false false true]]
;;     [2 [false false]]
;;     [1 [true]]
;;     [8 [true false false true false false false false]]
;;     [1 [true]])
(gen'/for [:parallel [n1 gen/nat
                      n2 gen/nat]
           :when ^{:max-tries 20} (coprime? n1 n2)
           :let [product (* n1 n2)]]
  {:n product, :factors [n1 n2]})

(gen/sample *1)
;; => ({:n 1, :factors [1 1]}
;;     {:n 0, :factors [1 0]}
;;     {:n 2, :factors [1 2]}
;;     {:n 0, :factors [0 1]}
;;     {:n 6, :factors [3 2]}
;;     {:n 20, :factors [4 5]}
;;     {:n 0, :factors [1 0]}
;;     {:n 4, :factors [1 4]}
;;     {:n 24, :factors [3 8]}
;;     {:n 14, :factors [2 7]})


string-from-regex is a suspiciously robust generator that will generate strings matching a regular expression:

user> (gen/sample (gen'/string-from-regex #"([☃-♥]{3}|B(A|OO)M)*"))

It does not work with every regular expression, but its goal is to correctly recognize (and report) the usage of unsupported features, and to handle supported features in a comprehensive way.


Generated strings shrink in a natural way:

(def gen-cool-string
   #"This string has (1 [A-Z]|[2-9]\d* [A-Z]'s)((, (1 [A-Z]|[2-9]\d* [A-Z]'s))*, and (1 [A-Z]|[2-9]\d* [A-Z]'s))?\."))

(def bad-prop
  (prop/for-all [s gen-cool-string]
    (not (re-find #"1 F" s))))

(t.c/quick-check 1000 bad-prop)
{:fail ["This string has 6309694848500700538 H's, 79102649012623413352 F's, 1 F, 59860 U's, 1 T, 1 W, 1 B, and 1 M."],
 :failing-size 26,
 :num-tests 27,
 :result false,
 :seed 1418877588316,
 :shrunk {:depth 8,
          :result false,
          :smallest ["This string has 1 A, 1 F, and 1 A."],
          :total-nodes-visited 27}}
Unsupported regex features

Some of these could be supported with a bit of effort.

  • All flags: (?i), (?s), etc.
  • Lookahead and lookbehind
  • Reluctant and Possesive quantifiers: X??, X*+, etc.
    • I'm not sure what these would mean anyhow
  • Anchors: \b, ^, \A, $...
  • Backreferences
    • This is tricky at least because it introduces the possibility of unmatchable expressions
  • Character class intersections
  • The hex syntax for unicode characters outside the BMP: \x{10001}
  • Named character classes: \p{IsAlphabetic}, \P{ASCII}, ...


com.gfredericks.test.chuck.properties/for-all is an alternative to clojure.test.check.properties/for-all that uses the for macro to interpret the binding clauses:

(require [com.gfredericks.test.chuck.properties :as prop'])

(prop'/for-all [a gen/pos-int
                :when (even? a)
                :let [b (/ a 2)]
                xs (gen/vector gen/int b)]
  (= (count xs) b))

Alternate clojure.test integration

The com.gfredericks.test.chuck.clojure-test namespace contains a couple macros that let you write property-based tests using the side-effecting (is ...) assertions normally used with clojure.test.

The checking macro is intended to be used with clojure.test/deftest:

(require '[clojure.test :refer [deftest is]]
         '[com.gfredericks.test.chuck.clojure-test :refer [checking]])

(deftest my-test
  (checking "that positive numbers are positive" 100
    [x gen/s-pos-int]
    (is (pos? x))
    (is (> x 0))))

The for-all macro is intended to be used with clojure.test.check.clojure-test/defspec:

(require '[clojure.test.check.clojure-test :refer [defspec]]
         '[com.gfredericks.test.chuck.clojure-test :refer [for-all]])

(defspec positive-number-positivity-spec 100
  (for-all [x gen/s-pos-int]
    (is (pos? x))
    (is (> x 0))))

More details in this blog post.


I welcome pull requests for any test.check utility that seems halfway reasonable.


Running tests

For clj, be sure to use leiningen 2.5.2. (so it picks up .cljc files) and do as usual:

$ lein test

For cljs bensu/doo is configured so the tests can be run with:

$ lein doo node node-test

Minimum required node version for lein doo is 0.12. It also works on 4.0.0. nvm might be used to switch node versions

To run with slimer.js, phantom or rhino:

# replace {js-env} with phantom, slimer or rhino
$ lein doo {js-env} test


  • @lackita for creating com.gfredericks.test.chuck.clojure-test
  • @weavejester for creating the original regex->string code
  • @miner for various help with the string-from-regex generator
  • @nberger for adapting to cljc format for ClojureScript, and general maintenance help


Copyright © 2016 Gary Fredericks

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.