ReddRadar
Agent skill
clojure-test-check
Property-based testing with clojure.test.check. Use when writing generative tests, creating custom generators, or debugging shrinking behavior. Triggers on test.check imports, prop/for-all, gen/* usage, or questions about property-based testing in Clojure.
Install this agent skill to your Project
npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/data/clojure-test-check
SKILL.md
test.check
Property-based testing generates random test data to verify properties hold across many inputs. Instead of specific test cases, define universal properties.
Core Pattern
(require '[clojure.test.check :as tc]
'[clojure.test.check.generators :as gen]
'[clojure.test.check.properties :as prop])
(def my-property
(prop/for-all [v (gen/vector gen/small-integer)]
(= (count v) (count (reverse v)))))
(tc/quick-check 100 my-property)
;; => {:result true, :pass? true, :num-tests 100, ...}
clojure.test Integration
(require '[clojure.test.check.clojure-test :refer [defspec]])
(defspec sort-is-idempotent ;; 100 optional iterations value here
(prop/for-all [v (gen/vector gen/small-integer)]
(= (sort v) (sort (sort v)))))
Important! Prefer NOT to supply an iterations, prefer the framework defaults
Essential Generators
| Generator | Produces |
|---|---|
gen/small-integer |
Integers bounded by size |
gen/large-integer |
Full range integers |
gen/nat |
Non-negative integers |
gen/boolean |
true/false |
gen/string |
Strings |
gen/keyword |
Keywords |
(gen/vector g) |
Vectors of g |
(gen/tuple g1 g2) |
Fixed heterogeneous vectors |
(gen/elements coll) |
Random element from coll |
(gen/one-of [g1 g2]) |
Choose generator randomly |
See references/cheatsheet.md for complete generator reference.
Generator Combinators
fmap - Transform generated values:
(gen/fmap sort (gen/vector gen/small-integer)) ; sorted vectors
(gen/fmap set (gen/vector gen/nat)) ; sets from vectors
such-that - Filter values (use sparingly, only for likely predicates):
(gen/such-that not-empty (gen/vector gen/boolean))
bind - Chain generators (value from first determines second):
(gen/bind (gen/not-empty (gen/vector gen/small-integer))
#(gen/tuple (gen/return %) (gen/elements %)))
let - Macro combining fmap/bind:
(gen/let [a gen/nat
b gen/nat]
{:sum (+ a b) :a a :b b})
Custom Record Generators
(defrecord User [name id email])
(def user-gen
(gen/fmap (partial apply ->User)
(gen/tuple gen/string-alphanumeric
gen/nat
(gen/fmap #(str % "@example.com") gen/string-alphanumeric))))
Recursive Generators
(def json-like
(gen/recursive-gen
(fn [inner] (gen/one-of [(gen/list inner)
(gen/map gen/keyword inner)]))
(gen/one-of [gen/small-integer gen/boolean gen/string])))
Shrinking Failures
When a test fails, test.check automatically shrinks to minimal failing case:
;; Fails on vectors containing 42
(tc/quick-check 100
(prop/for-all [v (gen/vector gen/small-integer)]
(not-any? #{42} v)))
;; :fail [[-35 -9 42 8 31 ...]] <- original failure
;; :shrunk {:smallest [[42]]} <- minimal case
Critical Pitfalls
Avoid gen/bind when gen/fmap suffices - bind hampers shrinking:
;; Bad: shrinks poorly
(gen/let [n (gen/fmap #(* 2 %) gen/nat)]
(gen/vector gen/large-integer n))
;; Good: shrinks well
(gen/fmap #(cond-> % (odd? (count %)) pop)
(gen/vector gen/large-integer))
Use gen/large-integer for real integer testing - small-integer/nat cap at ~200.
Run at least 100 tests - Size cycles through 0-199, fewer tests means poor coverage.
Don't use such-that for unlikely predicates - Will timeout. Use fmap to construct valid values instead.
See references/advanced.md for sizing/shrinking details.
Common Property Patterns
Roundtrip: (= x (decode (encode x)))
Idempotence: (= (f x) (f (f x)))
Invariant preservation: (= (count v) (count (sort v)))
Commutativity: (= (f a b) (f b a))
Model comparison: (= (my-impl x) (reference-impl x))
See references/examples.md for generator recipes.
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