diff --git a/tests/CSSList/AtRuleBlockListTest.php b/tests/CSSList/AtRuleBlockListTest.php
index b7f1610d..48e6e578 100644
--- a/tests/CSSList/AtRuleBlockListTest.php
+++ b/tests/CSSList/AtRuleBlockListTest.php
@@ -3,13 +3,46 @@
 namespace Sabberworm\CSS\Tests\CSSList;
 
 use PHPUnit\Framework\TestCase;
+use Sabberworm\CSS\Comment\Commentable;
+use Sabberworm\CSS\CSSList\AtRuleBlockList;
 use Sabberworm\CSS\Parser;
+use Sabberworm\CSS\Renderable;
 
 /**
  * @covers \Sabberworm\CSS\CSSList\AtRuleBlockList
  */
 class AtRuleBlockListTest extends TestCase
 {
+    /**
+     * @test
+     */
+    public function implementsAtRule()
+    {
+        $subject = new AtRuleBlockList('');
+
+        self::assertInstanceOf(AtRuleBlockList::class, $subject);
+    }
+
+    /**
+     * @test
+     */
+    public function implementsRenderable()
+    {
+        $subject = new AtRuleBlockList('');
+
+        self::assertInstanceOf(Renderable::class, $subject);
+    }
+
+    /**
+     * @test
+     */
+    public function implementsCommentable()
+    {
+        $subject = new AtRuleBlockList('');
+
+        self::assertInstanceOf(Commentable::class, $subject);
+    }
+
     /**
      * @return array<string, array<int, string>>
      */
diff --git a/tests/CSSList/DocumentTest.php b/tests/CSSList/DocumentTest.php
index c4071a25..a727400b 100644
--- a/tests/CSSList/DocumentTest.php
+++ b/tests/CSSList/DocumentTest.php
@@ -3,7 +3,9 @@
 namespace Sabberworm\CSS\Tests\CSSList;
 
 use PHPUnit\Framework\TestCase;
+use Sabberworm\CSS\Comment\Commentable;
 use Sabberworm\CSS\CSSList\Document;
+use Sabberworm\CSS\Renderable;
 use Sabberworm\CSS\RuleSet\DeclarationBlock;
 
 /**
@@ -21,6 +23,22 @@ protected function setUp()
         $this->subject = new Document();
     }
 
+    /**
+     * @test
+     */
+    public function implementsRenderable()
+    {
+        self::assertInstanceOf(Renderable::class, $this->subject);
+    }
+
+    /**
+     * @test
+     */
+    public function implementsCommentable()
+    {
+        self::assertInstanceOf(Commentable::class, $this->subject);
+    }
+
     /**
      * @test
      */
diff --git a/tests/CSSList/KeyFrameTest.php b/tests/CSSList/KeyFrameTest.php
new file mode 100644
index 00000000..080d5f94
--- /dev/null
+++ b/tests/CSSList/KeyFrameTest.php
@@ -0,0 +1,49 @@
+<?php
+
+namespace Sabberworm\CSS\Tests\CSSList;
+
+use PHPUnit\Framework\TestCase;
+use Sabberworm\CSS\Comment\Commentable;
+use Sabberworm\CSS\CSSList\KeyFrame;
+use Sabberworm\CSS\Property\AtRule;
+use Sabberworm\CSS\Renderable;
+
+/**
+ * @covers \Sabberworm\CSS\CSSList\KeyFrame
+ */
+class KeyFrameTest extends TestCase
+{
+    /**
+     * @var KeyFrame
+     */
+    protected $subject;
+
+    protected function setUp()
+    {
+        $this->subject = new KeyFrame();
+    }
+
+    /**
+     * @test
+     */
+    public function implementsAtRule()
+    {
+        self::assertInstanceOf(AtRule::class, $this->subject);
+    }
+
+    /**
+     * @test
+     */
+    public function implementsRenderable()
+    {
+        self::assertInstanceOf(Renderable::class, $this->subject);
+    }
+
+    /**
+     * @test
+     */
+    public function implementsCommentable()
+    {
+        self::assertInstanceOf(Commentable::class, $this->subject);
+    }
+}