diff --git a/tests/Unit/CSSList/DocumentTest.php b/tests/Unit/CSSList/DocumentTest.php
index ed1a2b22..07afcf1b 100644
--- a/tests/Unit/CSSList/DocumentTest.php
+++ b/tests/Unit/CSSList/DocumentTest.php
@@ -13,6 +13,7 @@
 use Sabberworm\CSS\Property\Charset;
 use Sabberworm\CSS\Property\Import;
 use Sabberworm\CSS\Renderable;
+use Sabberworm\CSS\RuleSet\AtRuleSet;
 use Sabberworm\CSS\RuleSet\DeclarationBlock;
 use Sabberworm\CSS\Value\CSSString;
 use Sabberworm\CSS\Value\URL;
@@ -148,6 +149,142 @@ public function getAllDeclarationBlocksIgnoresCharset(): void
         self::assertSame([], $result);
     }
 
+    /**
+     * @test
+     */
+    public function getAllRuleSetsWhenNoContentSetReturnsEmptyArray(): void
+    {
+        $subject = new Document();
+
+        self::assertSame([], $subject->getAllRuleSets());
+    }
+
+    /**
+     * @test
+     */
+    public function getAllRuleSetsReturnsOneDeclarationBlockDirectlySetAsContent(): void
+    {
+        $subject = new Document();
+
+        $declarationBlock = new DeclarationBlock();
+        $subject->setContents([$declarationBlock]);
+
+        $result = $subject->getAllRuleSets();
+
+        self::assertSame([$declarationBlock], $result);
+    }
+
+    /**
+     * @test
+     */
+    public function getAllRuleSetsReturnsOneAtRuleSetDirectlySetAsContent(): void
+    {
+        $subject = new Document();
+
+        $atRuleSet = new AtRuleSet('media');
+        $subject->setContents([$atRuleSet]);
+
+        $result = $subject->getAllRuleSets();
+
+        self::assertSame([$atRuleSet], $result);
+    }
+
+    /**
+     * @test
+     */
+    public function getAllRuleSetsReturnsMultipleDeclarationBlocksDirectlySetAsContents(): void
+    {
+        $subject = new Document();
+
+        $declarationBlock1 = new DeclarationBlock();
+        $declarationBlock2 = new DeclarationBlock();
+        $subject->setContents([$declarationBlock1, $declarationBlock2]);
+
+        $result = $subject->getAllRuleSets();
+
+        self::assertSame([$declarationBlock1, $declarationBlock2], $result);
+    }
+
+    /**
+     * @test
+     */
+    public function getAllRuleSetsReturnsMultipleAtRuleSetsDirectlySetAsContents(): void
+    {
+        $subject = new Document();
+
+        $atRuleSet1 = new AtRuleSet('media');
+        $atRuleSet2 = new AtRuleSet('media');
+        $subject->setContents([$atRuleSet1, $atRuleSet2]);
+
+        $result = $subject->getAllRuleSets();
+
+        self::assertSame([$atRuleSet1, $atRuleSet2], $result);
+    }
+
+    /**
+     * @test
+     */
+    public function getAllRuleSetsReturnsDeclarationBlocksWithinAtRuleBlockList(): void
+    {
+        $subject = new Document();
+
+        $declarationBlock = new DeclarationBlock();
+        $atRuleBlockList = new AtRuleBlockList('media');
+        $atRuleBlockList->setContents([$declarationBlock]);
+        $subject->setContents([$atRuleBlockList]);
+
+        $result = $subject->getAllRuleSets();
+
+        self::assertSame([$declarationBlock], $result);
+    }
+
+    /**
+     * @test
+     */
+    public function getAllRuleSetsReturnsAtRuleSetsWithinAtRuleBlockList(): void
+    {
+        $subject = new Document();
+
+        $atRule = new AtRuleSet('media');
+        $atRuleBlockList = new AtRuleBlockList('media');
+        $atRuleBlockList->setContents([$atRule]);
+        $subject->setContents([$atRuleBlockList]);
+
+        $result = $subject->getAllRuleSets();
+
+        self::assertSame([$atRule], $result);
+    }
+
+    /**
+     * @test
+     */
+    public function getAllRuleSetsIgnoresImport(): void
+    {
+        $subject = new Document();
+
+        $import = new Import(new URL(new CSSString('https://www.example.com/')), '');
+        $subject->setContents([$import]);
+
+        $result = $subject->getAllRuleSets();
+
+        self::assertSame([], $result);
+    }
+
+    /**
+     * @test
+     */
+    public function getAllRuleSetsIgnoresCharset(): void
+    {
+        $subject = new Document();
+
+        $charset = new Charset(new CSSString('UTF-8'));
+        $subject->setContents([$charset]);
+
+        $result = $subject->getAllRuleSets();
+
+        self::assertSame([], $result);
+    }
+
     /**
      * @test
      */