diff --git a/tests/src/AttributesMapTest.php b/tests/src/AttributesMapTest.php
index 267e468..dbc76bd 100644
--- a/tests/src/AttributesMapTest.php
+++ b/tests/src/AttributesMapTest.php
@@ -13,5 +13,9 @@ function testMerge() {
     $b = StaticAttributesMap::create(
       ['c0' => ['id' => 'c0id_b']],
       ['c0' => ['c0class_b' => 'c0class_b']]);
+    $merged = $a->merge($b);
+    $this->assertSame(
+      ' id="c0id" class="c0class c0class_b"',
+      $merged->nameGetAttributes('c0')->renderAttributes());
   }
 }