Add fn properties test helpers

src/com/gfredericks/schpec/fns.clj

@@ -0,0 +1,27 @@
+(ns com.gfredericks.schpec.fns)
+
+(defn commutative
+  "Returns a mapping fn suitable for use in clojure.spec.test/check that
+   specifies the given fn is commutative"
+  [f]
+  (fn [mapping]
+    (let [{:keys [args ret]} mapping]
+      (if (> (count args) 1)
+        (= ret (apply f (reverse args)))
+        true))))
+
+(defn associative
+  "Returns a mapping fn suitable for use in clojure.spec.test/check that
+   specifies the given fn is associative"
+  [f]
+  (fn [mapping]
+    (let [{:keys [args ret]} mapping]
+      (= ret (f (first args) (apply f (rest args)))))))
+
+(defn has-identity
+  "Returns a mapping fn suitable for use in clojure.spec.test/check that
+   specifies the given fn has the given identity value"
+  [f i]
+  (fn [mapping]
+    (let [{:keys [args ret]} mapping]
+      (= ret (f i ret)))))

test/com/gfredericks/schpec/fns_test.clj

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+(ns com.gfredericks.schpec.fns-test
+  (:require [clojure.test :refer :all]
+            [com.gfredericks.schpec.fns :refer :all]))
+
+(deftest test-commutative
+  (let [f (commutative +)]
+    (is (f {:args [1 2]
+            :ret 3})))
+  (let [f (commutative -)]
+    (is (not (f {:args [1 2]
+                 :ret -1})))))
+
+(deftest test-associative
+  (let [f (associative +)]
+    (is (f {:args [1 2 3]
+            :ret 6})))
+  (let [f (associative -)]
+    (is (not (f {:args [1 2 3]
+                 :ret -4})))))
+
+(deftest test-has-identity
+  (let [f (has-identity + 0)]
+    (is (f {:args [1 2]
+            :ret 3})))
+  (let [f (has-identity + 1)]
+    (is (not (f {:args [1 2]
+                 :ret 3})))))