Test cons (#780)

This closes #203.

Author: super7ramp

test/clojure/core_test/cons.cljc

@@ -0,0 +1,37 @@
+(ns clojure.core-test.cons
+  (:require [clojure.test :refer [deftest testing is are]]
+            [clojure.core-test.portability #?(:cljs :refer-macros :default :refer) [when-var-exists]]))
+
+(when-var-exists cons
+  (deftest test-cons
+
+    (testing "finite seqs"
+      (are [x seq expected] (= expected (cons x seq))
+                            1 [2 3] [1 2 3]
+                            1 '(2 3) [1 2 3]
+                            \1 "23" [\1 \2 \3]
+                            1 (sorted-set 1 2 3) [1 1 2 3]
+                            1 {:2 2 :3 3} [1 [:2 2] [:3 3]]
+                            [0 1] '(2 3) [[0 1] 2 3]))
+
+    (testing "infinite seqs"
+      (is (= -1 (first (cons -1 (range))))))
+
+    (testing "nil and empty"
+      (are [x seq expected] (= expected (cons x seq))
+                            nil nil [nil]
+                            1 nil [1]
+                            1 "" [1]
+                            1 '() [1]
+                            1 #{} [1]
+                            1 {} [1]
+                            1 [] [1]))
+
+    (testing "bad shape"
+      (are [seq] (thrown? #?(:cljs js/Error :default Exception) (cons 1 seq))
+                 :k
+                 42
+                 3.14
+                 true
+                 false
+                 cons))))