Test peek (#778)

This closes #393.

Author: super7ramp

test/clojure/core_test/peek.cljc

@@ -0,0 +1,26 @@
+(ns clojure.core-test.peek
+  (:require [clojure.test :refer [deftest testing is are]]
+            [clojure.core-test.portability #?(:cljs :refer-macros :default :refer) [when-var-exists]]))
+
+(when-var-exists clojure.core/peek
+  (deftest test-peek
+
+    (testing "list"
+      (is (nil? (peek '())))
+      (is (= :a (peek '(:a :b :c)))))
+
+    (testing "vector"
+      (is (nil? (peek [])))
+      (is (= :c (peek [:a :b :c]))))
+
+    (testing "nil"
+      (is (nil? (peek nil))))
+
+    (testing "bad shape"
+      (are [coll] (thrown? #?(:cljs js/Error :default Exception) (peek coll))
+                  #{1 2 3}
+                  {:a 1 :b 2}
+                  (cons 1 '())
+                  (range 10)
+                  "str"
+                  42))))