diff --git a/src/Test/TagRewriterTestCase.php b/src/Test/TagRewriterTestCase.php
new file mode 100644
index 0000000..1b99daf
--- /dev/null
+++ b/src/Test/TagRewriterTestCase.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace Webfactory\Html5TagRewriter\Test;
+
+use Override;
+use PHPUnit\Framework\TestCase;
+use Webfactory\Html5TagRewriter\Implementation\Html5TagRewriter;
+use Webfactory\Html5TagRewriter\TagRewriter;
+
+abstract class TagRewriterTestCase extends TestCase
+{
+    protected TagRewriter $rewriter;
+
+    #[Override]
+    protected function setUp(): void
+    {
+        $this->rewriter = new Html5TagRewriter();
+    }
+
+    public function assertRewriteResultEquals(string $expected, string $input): void
+    {
+        $result = $this->rewriter->processFragment($input);
+
+        $this->assertXmlStringEqualsXmlString($expected, $result);
+    }
+
+    public function assertRewriteResultUnchanged(string $input): void
+    {
+        $this->assertRewriteResultEquals($input, $input);
+    }
+}
diff --git a/tests/Html5TagRewriterTest.php b/tests/Implementation/Html5TagRewriterTest.php
similarity index 99%
rename from tests/Html5TagRewriterTest.php
rename to tests/Implementation/Html5TagRewriterTest.php
index 70b6edf..3561c4e 100644
--- a/tests/Html5TagRewriterTest.php
+++ b/tests/Implementation/Html5TagRewriterTest.php
@@ -2,7 +2,7 @@
 
 declare(strict_types=1);
 
-namespace Webfactory\Html5TagRewriter\Tests;
+namespace Webfactory\Html5TagRewriter\Tests\Implementation;
 
 use Dom\Element;
 use PHPUnit\Framework\Attributes\DataProvider;
diff --git a/tests/Test/TagRewriterTestCaseTest.php b/tests/Test/TagRewriterTestCaseTest.php
new file mode 100644
index 0000000..1aa5ec2
--- /dev/null
+++ b/tests/Test/TagRewriterTestCaseTest.php
@@ -0,0 +1,52 @@
+<?php
+
+namespace Webfactory\Html5TagRewriter\Tests\Test;
+
+use Dom\Element;
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\ExpectationFailedException;
+use Webfactory\Html5TagRewriter\Test\TagRewriterTestCase;
+use Webfactory\Html5TagRewriter\Tests\Fixtures\TestRewriteHandler;
+
+class TagRewriterTestCaseTest extends TagRewriterTestCase
+{
+    #[Test]
+    public function assertRewriteResultEquals_when_RewriteHandler_registered(): void
+    {
+        $handler = new TestRewriteHandler('//html:p');
+        $handler->onMatch(function (Element $element) {
+            $element->textContent = 'bar';
+        });
+        $this->rewriter->register($handler);
+
+        $this->assertRewriteResultEquals('<p>bar</p>', '<p>foo</p>');
+    }
+
+    #[Test]
+    public function assertRewriteResultEquals_when_no_RewriteHandler_fails(): void
+    {
+        $this->expectException(ExpectationFailedException::class);
+
+        $this->assertRewriteResultEquals('<p>bar</p>', '<p>foo</p>');
+    }
+
+    #[Test]
+    public function assertRewriteResultUnchanged_fails_when_RewriteHandler_registered(): void
+    {
+        $handler = new TestRewriteHandler('//html:p');
+        $handler->onMatch(function (Element $element) {
+            $element->textContent = 'bar';
+        });
+        $this->rewriter->register($handler);
+
+        $this->expectException(ExpectationFailedException::class);
+
+        $this->assertRewriteResultUnchanged('<p>foo</p>');
+    }
+
+    #[Test]
+    public function assertRewriteResultUnchanged_when_no_RewriteHandler_fails(): void
+    {
+        $this->assertRewriteResultUnchanged('<p>bar</p>', '<p>foo</p>');
+    }
+}