let's see if a warning is triggered by this new test

Tests/Util/TempFileUtilTest.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace Craue\FormFlowBundle\Tests\Util;
+
+use Craue\FormFlowBundle\Util\TempFileUtil;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @group unit
+ *
+ * @author Christian Raue <christian.raue@gmail.com>
+ * @copyright 2011-2020 Christian Raue
+ * @license http://opensource.org/licenses/mit-license.php MIT License
+ */
+class TempFileUtilTest extends TestCase {
+
+	public function testAddAndRemoveFiles() {
+		$tempFile = tempnam(sys_get_temp_dir(), 'craue_form_flow_temp_file');
+		$this->assertFileExists($tempFile);
+
+		TempFileUtil::addTempFile($tempFile);
+		$this->assertCount(1, $this->getTempFiles());
+
+		// add same file again to ensure that no warning is triggered while trying to remove a non-existing file
+		TempFileUtil::addTempFile($tempFile);
+		$this->assertCount(2, $this->getTempFiles());
+
+		TempFileUtil::removeTempFiles();
+		$this->assertCount(0, $this->getTempFiles());
+		$this->assertFileNotExists($tempFile);
+	}
+
+	private function getTempFiles() {
+		$reflectionClass = new \ReflectionClass(TempFileUtil::class);
+		$staticProperties = $reflectionClass->getStaticProperties();
+
+		return $staticProperties['tempFiles'];
+	}
+
+}