add sanitizer integration test

tests/integration/SanitizerTest.php

@@ -0,0 +1,13 @@
+<?php
+use PHPUnit\Framework\TestCase;
+
+/** @group integration */
+final class SanitizerTest extends TestCase {
+	public function test_sanitize_non_ascii(): void {
+		$this->assertEquals(
+			'<p>&#20013;&#25991;</p>',
+			Sanitizer::sanitize('<p>中文</p>')
+		);
+	}
+}
+