diff --git a/core/utils.test.ts b/core/utils.test.ts
index 6a1dde6..1969613 100644
--- a/core/utils.test.ts
+++ b/core/utils.test.ts
@@ -1,6 +1,6 @@
 import { assertEquals } from "testing/asserts.ts";
 
-import { isNil, isSkip } from "./utils.ts";
+import { concat, isNil, isSkip, join } from "./utils.ts";
 
 Deno.test({
   name: "should check value on nil",
@@ -27,3 +27,25 @@ Deno.test({
     assertEquals(isSkip([]), false);
   },
 });
+
+Deno.test({
+  name: "should return joined array",
+  fn: () => {
+    assertEquals(join(" ", ["hello", "world"]), "hello world");
+    assertEquals(
+      join(" ", ["hello", "", null, undefined, false, "world"]),
+      "hello world",
+    );
+  },
+});
+
+Deno.test({
+  name: "should return concated array",
+  fn: () => {
+    assertEquals(concat(["hello", "world"]), "helloworld");
+    assertEquals(
+      concat(["hello", "", null, undefined, false, "world"]),
+      "helloworld",
+    );
+  },
+});
diff --git a/ren/str.test.ts b/ren/str.test.ts
index f26dae7..d44e9c9 100644
--- a/ren/str.test.ts
+++ b/ren/str.test.ts
@@ -121,7 +121,7 @@ Deno.test({
 });
 
 Deno.test({
-  name: "should force render doctype if root nod is not html",
+  name: "should force render doctype if root node is not html",
   fn: () => {
     const layout = E("body", [], []);