diff --git a/tests/Unit/CSSList/AtRuleBlockListTest.php b/tests/Unit/CSSList/AtRuleBlockListTest.php
index 86411142d..1e587f8e9 100644
--- a/tests/Unit/CSSList/AtRuleBlockListTest.php
+++ b/tests/Unit/CSSList/AtRuleBlockListTest.php
@@ -7,6 +7,7 @@
 use PHPUnit\Framework\TestCase;
 use Sabberworm\CSS\Comment\Commentable;
 use Sabberworm\CSS\CSSList\AtRuleBlockList;
+use Sabberworm\CSS\CSSList\CSSBlockList;
 use Sabberworm\CSS\CSSList\CSSList;
 use Sabberworm\CSS\Renderable;
 
@@ -51,6 +52,16 @@ public function implementsCommentable(): void
         self::assertInstanceOf(Commentable::class, $subject);
     }
 
+    /**
+     * @test
+     */
+    public function isCSSBLockList(): void
+    {
+        $subject = new AtRuleBlockList('supports');
+
+        self::assertInstanceOf(CSSBlockList::class, $subject);
+    }
+
     /**
      * @test
      */
diff --git a/tests/Unit/CSSList/CSSBlockListTest.php b/tests/Unit/CSSList/CSSBlockListTest.php
new file mode 100644
index 000000000..9d7ef076b
--- /dev/null
+++ b/tests/Unit/CSSList/CSSBlockListTest.php
@@ -0,0 +1,48 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabberworm\CSS\Tests\Unit\CSSList;
+
+use PHPUnit\Framework\TestCase;
+use Sabberworm\CSS\Comment\Commentable;
+use Sabberworm\CSS\CSSList\CSSList;
+use Sabberworm\CSS\Renderable;
+use Sabberworm\CSS\Tests\Unit\CSSList\Fixtures\ConcreteCSSBlockList;
+
+/**
+ * @covers \Sabberworm\CSS\CSSList\CSSBlockList
+ * @covers \Sabberworm\CSS\CSSList\CSSList
+ */
+final class CSSBlockListTest extends TestCase
+{
+    /**
+     * @test
+     */
+    public function implementsRenderable(): void
+    {
+        $subject = new ConcreteCSSBlockList();
+
+        self::assertInstanceOf(Renderable::class, $subject);
+    }
+
+    /**
+     * @test
+     */
+    public function implementsCommentable(): void
+    {
+        $subject = new ConcreteCSSBlockList();
+
+        self::assertInstanceOf(Commentable::class, $subject);
+    }
+
+    /**
+     * @test
+     */
+    public function isCSSList(): void
+    {
+        $subject = new ConcreteCSSBlockList();
+
+        self::assertInstanceOf(CSSList::class, $subject);
+    }
+}
diff --git a/tests/Unit/CSSList/DocumentTest.php b/tests/Unit/CSSList/DocumentTest.php
index 5ac66b5b1..00158590b 100644
--- a/tests/Unit/CSSList/DocumentTest.php
+++ b/tests/Unit/CSSList/DocumentTest.php
@@ -7,6 +7,7 @@
 use PHPUnit\Framework\TestCase;
 use Sabberworm\CSS\Comment\Commentable;
 use Sabberworm\CSS\CSSList\AtRuleBlockList;
+use Sabberworm\CSS\CSSList\CSSBlockList;
 use Sabberworm\CSS\CSSList\CSSList;
 use Sabberworm\CSS\CSSList\Document;
 use Sabberworm\CSS\Property\Charset;
@@ -43,6 +44,16 @@ public function implementsCommentable(): void
         self::assertInstanceOf(Commentable::class, new Document());
     }
 
+    /**
+     * @test
+     */
+    public function isCSSBlockList(): void
+    {
+        $subject = new Document();
+
+        self::assertInstanceOf(CSSBlockList::class, $subject);
+    }
+
     /**
      * @test
      */
diff --git a/tests/Unit/CSSList/Fixtures/ConcreteCSSBlockList.php b/tests/Unit/CSSList/Fixtures/ConcreteCSSBlockList.php
new file mode 100644
index 000000000..956c7036a
--- /dev/null
+++ b/tests/Unit/CSSList/Fixtures/ConcreteCSSBlockList.php
@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabberworm\CSS\Tests\Unit\CSSList\Fixtures;
+
+use Sabberworm\CSS\CSSList\CSSBlockList;
+use Sabberworm\CSS\OutputFormat;
+
+final class ConcreteCSSBlockList extends CSSBlockList
+{
+    public function isRootList(): bool
+    {
+        throw new \BadMethodCallException('Not implemented', 1740395831);
+    }
+
+    public function render(OutputFormat $outputFormat): string
+    {
+        throw new \BadMethodCallException('Not implemented', 1740395836);
+    }
+}