From 65d9a4284454ee4279612e15e3ae9d55598ed21a Mon Sep 17 00:00:00 2001
From: christos chatzifountas <christos.chatzifountas@biotz.io>
Date: Mon, 29 Sep 2025 08:40:23 +0300
Subject: [PATCH] test `mapcat` (#354)

---
 test/clojure/core_test/mapcat.cljc | 54 ++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)
 create mode 100644 test/clojure/core_test/mapcat.cljc

diff --git a/test/clojure/core_test/mapcat.cljc b/test/clojure/core_test/mapcat.cljc
new file mode 100644
index 0000000..8a20f28
--- /dev/null
+++ b/test/clojure/core_test/mapcat.cljc
@@ -0,0 +1,54 @@
+(ns clojure.core-test.mapcat
+  (:require [clojure.test :as t :refer [deftest testing is are]]
+            [clojure.core-test.portability #?(:cljs :refer-macros :default :refer) [when-var-exists]]))
+
+
+(when-var-exists mapcat
+  (deftest common-cases
+    (testing "nil input"
+      (is (nil? (seq (mapcat identity nil)))))
+    (testing "concatenation"
+      (is (= [1 2 3 4] (mapcat identity [[1 2] '(3 4)]))))
+    (testing "function producing seqs"
+      (is (= [0 0 1 0 1 2] (mapcat #(range %) [1 2 3]))))
+    (testing "empty results contribute nothing"
+      (is (= [2] (mapcat (fn [x] (if (odd? x) [] [x])) [1 2 3]))))
+    (testing "strings"
+      (is (= [\a \b \c] (mapcat identity ["ab" "" "c"]))))
+    (testing "as transducer"
+      (is (= [1 1 2 2 3 3] (transduce (mapcat #(repeat 2 %)) conj [] [1 2 3]))))
+    (testing "into with transducer"
+      (is (= [0 0 1 1 2 2] (into [] (mapcat #(repeat 2 %)) (range 3)))))
+    (testing "incorrect shape"
+      (is (thrown? #?(:cljs :default :clj Exception :cljr Exception)
+                   (mapcat identity 5))))
+    (testing "infinite input laziness"
+      (is (= [0 0 1 1 2]  (take 5  (mapcat #(repeat 2 %) (range))))))
+    (testing "empty collection input"
+      (is (= [] (mapcat identity []))))
+    (testing "single element producing empty sequence"
+      (is (= [] (mapcat (constantly []) [42]))))
+    (testing "single element producing seq"
+      (is (= [99] (mapcat list [99]))))
+    (testing "function returns a string (seqable)"
+      (is (= [\h \i] (mapcat identity ["hi"]))))
+    (testing "flatten key/value pairs"
+        (is (= [:a 1 :b 2 :c 3] (mapcat identity {:a 1 :b 2 :c 3}))))
+    (testing "function returns nil"
+      (is (= [] (mapcat (constantly nil) [1 2 3]))))
+    (testing "two collections zipped, function applied to pairs"
+      (is (= [2 2 4 4 6 6] (mapcat (fn [x y] [(* 2 x) (* 2 y)]) [1 2 3] [1 2 3]))))
+    (testing "one collection shorter than the other"
+      (is (= [2 4] (mapcat (fn [x y] [(* x y)]) [1 2] [2 2 2]))))
+    (testing "works lazily on infinite input"
+      (is (= [0 1 2 3 4 5] (->> (mapcat (fn [x] [x]) (range)) (take 6)))))
+    (testing "function sometimes returns []"
+      (is (= [1 3 5] (mapcat #(if (odd? %) [%] []) (range 1 6)))))
+    (testing "function sometimes returns nil"
+      (is (= [2 4] (mapcat #(if (even? %) [%] nil) (range 1 5)))))
+    (testing "non-seqable second arg"
+      (is (thrown? #?(:cljs :default :clj Exception :cljr Exception)
+                   (mapcat identity 5))))
+    (testing "non-function first arg"
+      (is (thrown? #?(:cljs :default :clj Exception :cljr Exception)
+                   (mapcat 42 [1 2]))))))