diff --git a/apps/workflowengine/tests/Check/FileMimeTypeTest.php b/apps/workflowengine/tests/Check/FileMimeTypeTest.php
new file mode 100644
index 0000000000..3ebcaa8f4b
--- /dev/null
+++ b/apps/workflowengine/tests/Check/FileMimeTypeTest.php
@@ -0,0 +1,192 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * @copyright Copyright (c) 2021 Robin Appelman <robin@icewind.nl>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+namespace OCA\WorkflowEngine\Tests\Check;
+
+use OC\Files\Storage\Temporary;
+use OCA\WorkflowEngine\Check\FileMimeType;
+use OCP\Files\IMimeTypeDetector;
+use OCP\IL10N;
+use OCP\IRequest;
+use Test\TestCase;
+
+class TemporaryNoLocal extends Temporary {
+	public function instanceOfStorage($className) {
+		if ($className === '\OC\Files\Storage\Local') {
+			return false;
+		} else {
+			return parent::instanceOfStorage($className);
+		}
+	}
+}
+
+/**
+ * @group DB
+ */
+class FileMimeTypeTest extends TestCase {
+	/** @var IL10N */
+	private $l10n;
+	/** @var IRequest */
+	private $request;
+	/** @var IMimeTypeDetector */
+	private $mimeDetector;
+
+	private $extensions = [
+		'.txt' => 'text/plain-path-detected',
+	];
+
+	private $content = [
+		'text-content' => 'text/plain-content-detected',
+	];
+
+	protected function setUp(): void {
+		parent::setUp();
+
+		$this->l10n = $this->createMock(IL10N::class);
+		$this->request = $this->createMock(IRequest::class);
+		$this->mimeDetector = $this->createMock(IMimeTypeDetector::class);
+		$this->mimeDetector->method('detectPath')
+			->willReturnCallback(function ($path) {
+				foreach ($this->extensions as $extension => $mime) {
+					if (strpos($path, $extension) !== false) {
+						return $mime;
+					}
+				}
+				return 'application/octet-stream';
+			});
+		$this->mimeDetector->method('detectContent')
+			->willReturnCallback(function ($path) {
+				$body = file_get_contents($path);
+				foreach ($this->content as $match => $mime) {
+					if (strpos($body, $match) !== false) {
+						return $mime;
+					}
+				}
+				return 'application/octet-stream';
+			});
+	}
+
+	public function testUseCachedMimetype() {
+		$storage = new Temporary([]);
+		$storage->mkdir('foo');
+		$storage->file_put_contents('foo/bar.txt', 'asd');
+		$storage->getScanner()->scan('');
+
+
+		$check = new FileMimeType($this->l10n, $this->request, $this->mimeDetector);
+		$check->setFileInfo($storage, 'foo/bar.txt');
+
+		$this->assertTrue($check->executeCheck('is', 'text/plain'));
+	}
+
+	public function testNonCachedNotExists() {
+		$storage = new Temporary([]);
+
+		$check = new FileMimeType($this->l10n, $this->request, $this->mimeDetector);
+		$check->setFileInfo($storage, 'foo/bar.txt');
+
+		$this->assertTrue($check->executeCheck('is', 'text/plain-path-detected'));
+	}
+
+	public function testNonCachedLocal() {
+		$storage = new Temporary([]);
+		$storage->mkdir('foo');
+		$storage->file_put_contents('foo/bar.txt', 'text-content');
+
+		$check = new FileMimeType($this->l10n, $this->request, $this->mimeDetector);
+		$check->setFileInfo($storage, 'foo/bar.txt');
+
+		$this->assertTrue($check->executeCheck('is', 'text/plain-content-detected'));
+	}
+
+	public function testNonCachedNotLocal() {
+		$storage = new TemporaryNoLocal([]);
+		$storage->mkdir('foo');
+		$storage->file_put_contents('foo/bar.txt', 'text-content');
+
+		$check = new FileMimeType($this->l10n, $this->request, $this->mimeDetector);
+		$check->setFileInfo($storage, 'foo/bar.txt');
+
+		$this->assertTrue($check->executeCheck('is', 'text/plain-path-detected'));
+	}
+
+	public function testFallback() {
+		$storage = new Temporary([]);
+
+		$check = new FileMimeType($this->l10n, $this->request, $this->mimeDetector);
+		$check->setFileInfo($storage, 'unknown');
+
+		$this->assertTrue($check->executeCheck('is', 'application/octet-stream'));
+	}
+
+	public function testFromCacheCached() {
+		$storage = new Temporary([]);
+		$storage->mkdir('foo');
+		$storage->file_put_contents('foo/bar.txt', 'asd');
+		$storage->getScanner()->scan('');
+
+		$check = new FileMimeType($this->l10n, $this->request, $this->mimeDetector);
+		$check->setFileInfo($storage, 'foo/bar.txt');
+
+		$this->assertTrue($check->executeCheck('is', 'text/plain'));
+
+		$storage->getCache()->clear();
+
+		$this->assertTrue($check->executeCheck('is', 'text/plain'));
+
+		$newCheck = new FileMimeType($this->l10n, $this->request, $this->mimeDetector);
+		$newCheck->setFileInfo($storage, 'foo/bar.txt');
+		$this->assertTrue($newCheck->executeCheck('is', 'text/plain-path-detected'));
+	}
+
+	public function testExistsCached() {
+		$storage = new TemporaryNoLocal([]);
+		$storage->mkdir('foo');
+		$storage->file_put_contents('foo/bar.txt', 'text-content');
+
+		$check = new FileMimeType($this->l10n, $this->request, $this->mimeDetector);
+		$check->setFileInfo($storage, 'foo/bar.txt');
+
+		$this->assertTrue($check->executeCheck('is', 'text/plain-content-detected'));
+		$storage->unlink('foo/bar.txt');
+		$this->assertTrue($check->executeCheck('is', 'text/plain-content-detected'));
+
+		$newCheck = new FileMimeType($this->l10n, $this->request, $this->mimeDetector);
+		$newCheck->setFileInfo($storage, 'foo/bar.txt');
+		$this->assertTrue($newCheck->executeCheck('is', 'text/plain-path-detected'));
+	}
+
+	public function testNonExistsNotCached() {
+		$storage = new TemporaryNoLocal([]);
+
+		$check = new FileMimeType($this->l10n, $this->request, $this->mimeDetector);
+		$check->setFileInfo($storage, 'foo/bar.txt');
+
+		$this->assertTrue($check->executeCheck('is', 'text/plain-path-detected'));
+
+		$storage->mkdir('foo');
+		$storage->file_put_contents('foo/bar.txt', 'text-content');
+
+		$this->assertTrue($check->executeCheck('is', 'text/plain-content-detected'));
+	}
+}