diff --git a/apps/files/tests/Controller/ApiControllerTest.php b/apps/files/tests/Controller/ApiControllerTest.php
index 4b7bec065a..56d0f6c8de 100644
--- a/apps/files/tests/Controller/ApiControllerTest.php
+++ b/apps/files/tests/Controller/ApiControllerTest.php
@@ -28,11 +28,15 @@ namespace OCA\Files\Controller;
 
 use OC\Files\FileInfo;
 use OCP\AppFramework\Http;
+use OCP\Files\File;
+use OCP\Files\Folder;
 use OCP\Files\NotFoundException;
+use OCP\Files\SimpleFS\ISimpleFile;
 use OCP\Files\StorageNotAvailableException;
 use OCP\IConfig;
 use OCP\IUser;
 use OCP\IUserSession;
+use OCP\Share\IManager;
 use Test\TestCase;
 use OCP\IRequest;
 use OCA\Files\Service\TagService;
@@ -54,7 +58,7 @@ class ApiControllerTest extends TestCase {
 	private $request;
 	/** @var TagService */
 	private $tagService;
-	/** @var IPreview */
+	/** @var IPreview|\PHPUnit_Framework_MockObject_MockObject */
 	private $preview;
 	/** @var ApiController */
 	private $apiController;
@@ -62,11 +66,13 @@ class ApiControllerTest extends TestCase {
 	private $shareManager;
 	/** @var \OCP\IConfig */
 	private $config;
-	/** @var  \OC\Files\Node\Folder */
+	/** @var Folder|\PHPUnit_Framework_MockObject_MockObject */
 	private $userFolder;
 
 	public function setUp() {
-		$this->request = $this->getMockBuilder('\OCP\IRequest')
+		parent::setUp();
+
+		$this->request = $this->getMockBuilder(IRequest::class)
 			->disableOriginalConstructor()
 			->getMock();
 		$this->user = $this->createMock(IUser::class);
@@ -77,17 +83,17 @@ class ApiControllerTest extends TestCase {
 		$userSession->expects($this->any())
 			->method('getUser')
 			->will($this->returnValue($this->user));
-		$this->tagService = $this->getMockBuilder('\OCA\Files\Service\TagService')
+		$this->tagService = $this->getMockBuilder(TagService::class)
 			->disableOriginalConstructor()
 			->getMock();
-		$this->shareManager = $this->getMockBuilder('\OCP\Share\IManager')
+		$this->shareManager = $this->getMockBuilder(IManager::class)
 			->disableOriginalConstructor()
 			->getMock();
-		$this->preview = $this->getMockBuilder('\OCP\IPreview')
+		$this->preview = $this->getMockBuilder(IPreview::class)
 			->disableOriginalConstructor()
 			->getMock();
 		$this->config = $this->createMock(IConfig::class);
-		$this->userFolder = $this->getMockBuilder('\OC\Files\Node\Folder')
+		$this->userFolder = $this->getMockBuilder(Folder::class)
 			->disableOriginalConstructor()
 			->getMock();
 
@@ -153,28 +159,41 @@ class ApiControllerTest extends TestCase {
 	}
 
 	public function testGetThumbnailInvalidSize() {
+		$this->userFolder->method('get')
+			->with($this->equalTo(''))
+			->willThrowException(new NotFoundException());
 		$expected = new DataResponse(['message' => 'Requested size must be numeric and a positive value.'], Http::STATUS_BAD_REQUEST);
 		$this->assertEquals($expected, $this->apiController->getThumbnail(0, 0, ''));
 	}
 
 	public function testGetThumbnailInvaidImage() {
+		$file = $this->createMock(File::class);
+		$this->userFolder->method('get')
+			->with($this->equalTo('unknown.jpg'))
+			->willReturn($file);
 		$this->preview->expects($this->once())
-			->method('createPreview')
-			->with('files/unknown.jpg', 10, 10, true)
-			->willReturn(new Image);
+			->method('getPreview')
+			->with($file, 10, 10, true)
+			->willThrowException(new NotFoundException());
 		$expected = new DataResponse(['message' => 'File not found.'], Http::STATUS_NOT_FOUND);
 		$this->assertEquals($expected, $this->apiController->getThumbnail(10, 10, 'unknown.jpg'));
 	}
 
 	public function testGetThumbnail() {
+		$file = $this->createMock(File::class);
+		$this->userFolder->method('get')
+			->with($this->equalTo('known.jpg'))
+			->willReturn($file);
+		$preview = $this->createMock(ISimpleFile::class);
 		$this->preview->expects($this->once())
-			->method('createPreview')
-			->with('files/known.jpg', 10, 10, true)
-			->willReturn(new Image(\OC::$SERVERROOT.'/tests/data/testimage.jpg'));
+			->method('getPreview')
+			->with($this->equalTo($file), 10, 10, true)
+			->willReturn($preview);
 
 		$ret = $this->apiController->getThumbnail(10, 10, 'known.jpg');
 
 		$this->assertEquals(Http::STATUS_OK, $ret->getStatus());
+		$this->assertInstanceOf(Http\FileDisplayResponse::class, $ret);
 	}
 
 	public function testUpdateFileSorting() {
diff --git a/lib/composer/composer/autoload_classmap.php b/lib/composer/composer/autoload_classmap.php
index 19905bdbe7..42cfb8c45e 100644
--- a/lib/composer/composer/autoload_classmap.php
+++ b/lib/composer/composer/autoload_classmap.php
@@ -622,6 +622,7 @@ return array(
     'OC\\Preview\\Font' => $baseDir . '/lib/private/Preview/Font.php',
     'OC\\Preview\\GIF' => $baseDir . '/lib/private/Preview/GIF.php',
     'OC\\Preview\\Generator' => $baseDir . '/lib/private/Preview/Generator.php',
+    'OC\\Preview\\GeneratorHelper' => $baseDir . '/lib/private/Preview/GeneratorHelper.php',
     'OC\\Preview\\Illustrator' => $baseDir . '/lib/private/Preview/Illustrator.php',
     'OC\\Preview\\Image' => $baseDir . '/lib/private/Preview/Image.php',
     'OC\\Preview\\JPEG' => $baseDir . '/lib/private/Preview/JPEG.php',
diff --git a/lib/composer/composer/autoload_static.php b/lib/composer/composer/autoload_static.php
index 82dba9c92f..d7e937577f 100644
--- a/lib/composer/composer/autoload_static.php
+++ b/lib/composer/composer/autoload_static.php
@@ -652,6 +652,7 @@ class ComposerStaticInit53792487c5a8370acc0b06b1a864ff4c
         'OC\\Preview\\Font' => __DIR__ . '/../../..' . '/lib/private/Preview/Font.php',
         'OC\\Preview\\GIF' => __DIR__ . '/../../..' . '/lib/private/Preview/GIF.php',
         'OC\\Preview\\Generator' => __DIR__ . '/../../..' . '/lib/private/Preview/Generator.php',
+        'OC\\Preview\\GeneratorHelper' => __DIR__ . '/../../..' . '/lib/private/Preview/GeneratorHelper.php',
         'OC\\Preview\\Illustrator' => __DIR__ . '/../../..' . '/lib/private/Preview/Illustrator.php',
         'OC\\Preview\\Image' => __DIR__ . '/../../..' . '/lib/private/Preview/Image.php',
         'OC\\Preview\\JPEG' => __DIR__ . '/../../..' . '/lib/private/Preview/JPEG.php',
diff --git a/lib/private/Preview/Generator.php b/lib/private/Preview/Generator.php
index d4c38b1cb6..3d4e9bf367 100644
--- a/lib/private/Preview/Generator.php
+++ b/lib/private/Preview/Generator.php
@@ -23,46 +23,43 @@
 
 namespace OC\Preview;
 
-use OC\Files\View;
 use OCP\Files\File;
 use OCP\Files\IAppData;
-use OCP\Files\IRootFolder;
 use OCP\Files\NotFoundException;
 use OCP\Files\SimpleFS\ISimpleFile;
 use OCP\Files\SimpleFS\ISimpleFolder;
 use OCP\IConfig;
 use OCP\IImage;
-use OCP\Image as img;
 use OCP\IPreview;
 use OCP\Preview\IProvider;
 
 class Generator {
 
-	/** @var IRootFolder*/
-	private $rootFolder;
 	/** @var IPreview */
 	private $previewManager;
 	/** @var IConfig */
 	private $config;
 	/** @var IAppData */
 	private $appData;
+	/** @var GeneratorHelper */
+	private $helper;
 
 	/**
-	 * @param IRootFolder $rootFolder
 	 * @param IConfig $config
 	 * @param IPreview $previewManager
 	 * @param IAppData $appData
+	 * @param GeneratorHelper $helper
 	 */
 	public function __construct(
-		IRootFolder $rootFolder,
 		IConfig $config,
 		IPreview $previewManager,
-		IAppData $appData
+		IAppData $appData,
+		GeneratorHelper $helper
 	) {
-		$this->rootFolder = $rootFolder;
 		$this->config = $config;
 		$this->previewManager = $previewManager;
 		$this->appData = $appData;
+		$this->helper = $helper;
 	}
 
 	/**
@@ -88,10 +85,6 @@ class Generator {
 			throw new NotFoundException();
 		}
 
-		/*
-		 * Get the preview folder
-		 * TODO: Separate preview creation from storing previews
-		 */
 		$previewFolder = $this->getPreviewFolder($file);
 
 		// Get the max preview and infer the max preview sizes from that
@@ -134,17 +127,15 @@ class Generator {
 			}
 
 			foreach ($providers as $provider) {
-				$provider = $provider();
+				$provider = $this->helper->getProvider($provider);
 				if (!($provider instanceof IProvider)) {
 					continue;
 				}
 
-				list($view, $path) = $this->getViewAndPath($file);
-
 				$maxWidth = (int)$this->config->getSystemValue('preview_max_x', 2048);
 				$maxHeight = (int)$this->config->getSystemValue('preview_max_y', 2048);
 
-				$preview = $provider->getThumbnail($path, $maxWidth, $maxHeight, false, $view);
+				$preview = $this->helper->getThumbnail($provider, $file, $maxWidth, $maxHeight);
 
 				if (!($preview instanceof IImage)) {
 					continue;
@@ -185,24 +176,7 @@ class Generator {
 		return $path;
 	}
 
-	/**
-	 * @param File $file
-	 * @return array
-	 * This is required to create the old view and path
-	 */
-	private function getViewAndPath(File $file) {
-		$owner = $file->getOwner()->getUID();
 
-		$userFolder = $this->rootFolder->getUserFolder($owner)->getParent();
-		$nodes = $userFolder->getById($file->getId());
-
-		$file = $nodes[0];
-
-		$view = new View($userFolder->getPath());
-		$path = $userFolder->getRelativePath($file->getPath());
-
-		return [$view, $path];
-	}
 
 	/**
 	 * @param int $width
@@ -300,7 +274,7 @@ class Generator {
 	 * @throws NotFoundException
 	 */
 	private function generatePreview(ISimpleFolder $previewFolder, ISimpleFile $maxPreview, $width, $height, $crop, $maxWidth, $maxHeight) {
-		$preview = new img($maxPreview->getContent());
+		$preview = $this->helper->getImage($maxPreview);
 
 		if ($crop) {
 			if ($height !== $preview->height() && $width !== $preview->width()) {
diff --git a/lib/private/Preview/GeneratorHelper.php b/lib/private/Preview/GeneratorHelper.php
new file mode 100644
index 0000000000..282c46a2a5
--- /dev/null
+++ b/lib/private/Preview/GeneratorHelper.php
@@ -0,0 +1,91 @@
+<?php
+/**
+ * @copyright Copyright (c) 2016, Roeland Jago Douma <roeland@famdouma.nl>
+ *
+ * @author Roeland Jago Douma <roeland@famdouma.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 OC\Preview;
+
+use OC\Files\View;
+use OCP\Files\File;
+use OCP\Files\IRootFolder;
+use OCP\Files\SimpleFS\ISimpleFile;
+use OCP\IImage;
+use OCP\Image as img;
+use OCP\Preview\IProvider;
+
+/**
+ * Very small wrapper class to make the generator fully unit testable
+ */
+class GeneratorHelper {
+
+	/** @var IRootFolder */
+	private $rootFolder;
+
+	public function __construct(IRootFolder $rootFolder) {
+		$this->rootFolder = $rootFolder;
+	}
+
+	/**
+	 * @param IProvider $provider
+	 * @param File $file
+	 * @param int $maxWidth
+	 * @param int $maxHeight
+	 * @return bool|IImage
+	 */
+	public function getThumbnail(IProvider $provider, File $file, $maxWidth, $maxHeight) {
+		list($view, $path) = $this->getViewAndPath($file);
+		return $provider->getThumbnail($path, $maxWidth, $maxHeight, false, $view);
+	}
+
+	/**
+	 * @param File $file
+	 * @return array
+	 * This is required to create the old view and path
+	 */
+	private function getViewAndPath(File $file) {
+		$owner = $file->getOwner()->getUID();
+
+		$userFolder = $this->rootFolder->getUserFolder($owner)->getParent();
+
+		$nodes = $userFolder->getById($file->getId());
+		$file = $nodes[0];
+
+		$view = new View($userFolder->getPath());
+		$path = $userFolder->getRelativePath($file->getPath());
+
+		return [$view, $path];
+	}
+
+	/**
+	 * @param ISimpleFile $maxPreview
+	 * @return IImage
+	 */
+	public function getImage(ISimpleFile $maxPreview) {
+		return new img($maxPreview->getContent());
+	}
+
+	/**
+	 * @param $provider
+	 * @return IProvider
+	 */
+	public function getProvider($provider) {
+		return $provider();
+	}
+}
diff --git a/lib/private/PreviewManager.php b/lib/private/PreviewManager.php
index 2c17a5f3c8..a2ef9659b3 100644
--- a/lib/private/PreviewManager.php
+++ b/lib/private/PreviewManager.php
@@ -26,6 +26,7 @@
 namespace OC;
 
 use OC\Preview\Generator;
+use OC\Preview\GeneratorHelper;
 use OCP\Files\File;
 use OCP\Files\IAppData;
 use OCP\Files\IRootFolder;
@@ -159,10 +160,12 @@ class PreviewManager implements IPreview {
 	public function getPreview(File $file, $width = -1, $height = -1, $crop = false, $mode = IPreview::MODE_FILL, $mimeType = null) {
 		if ($this->generator === null) {
 			$this->generator = new Generator(
-				$this->rootFolder,
 				$this->config,
 				$this,
-				$this->appData
+				$this->appData,
+				new GeneratorHelper(
+					$this->rootFolder
+				)
 			);
 		}
 
diff --git a/tests/lib/Preview/GeneratorTest.php b/tests/lib/Preview/GeneratorTest.php
new file mode 100644
index 0000000000..d64a0b912e
--- /dev/null
+++ b/tests/lib/Preview/GeneratorTest.php
@@ -0,0 +1,338 @@
+<?php
+/**
+ * @copyright Copyright (c) 2016, Roeland Jago Douma <roeland@famdouma.nl>
+ *
+ * @author Roeland Jago Douma <roeland@famdouma.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 Test\Preview;
+
+use OC\Preview\Generator;
+use OC\Preview\GeneratorHelper;
+use OCP\Files\File;
+use OCP\Files\IAppData;
+use OCP\Files\NotFoundException;
+use OCP\Files\SimpleFS\ISimpleFile;
+use OCP\Files\SimpleFS\ISimpleFolder;
+use OCP\IConfig;
+use OCP\IImage;
+use OCP\IPreview;
+use OCP\Preview\IProvider;
+
+class GeneratorTest extends \Test\TestCase {
+
+	/** @var IConfig|\PHPUnit_Framework_MockObject_MockObject */
+	private $config;
+
+	/** @var IPreview|\PHPUnit_Framework_MockObject_MockObject */
+	private $previewManager;
+
+	/** @var IAppData|\PHPUnit_Framework_MockObject_MockObject */
+	private $appData;
+
+	/** @var GeneratorHelper|\PHPUnit_Framework_MockObject_MockObject */
+	private $helper;
+
+	/** @var Generator */
+	private $generator;
+
+	public function setUp() {
+		parent::setUp();
+
+		$this->config = $this->createMock(IConfig::class);
+		$this->previewManager = $this->createMock(IPreview::class);
+		$this->appData = $this->createMock(IAppData::class);
+		$this->helper = $this->createMock(GeneratorHelper::class);
+
+		$this->generator = new Generator(
+			$this->config,
+			$this->previewManager,
+			$this->appData,
+			$this->helper
+		);
+	}
+
+	public function testGetCachedPreview() {
+		$file = $this->createMock(File::class);
+		$file->method('getMimeType')
+			->willReturn('myMimeType');
+		$file->method('getId')
+			->willReturn(42);
+
+		$this->previewManager->method('isMimeSupported')
+			->with($this->equalTo('myMimeType'))
+			->willReturn(true);
+
+		$previewFolder = $this->createMock(ISimpleFolder::class);
+		$this->appData->method('getFolder')
+			->with($this->equalTo(42))
+			->willReturn($previewFolder);
+
+		$maxPreview = $this->createMock(ISimpleFile::class);
+		$maxPreview->method('getName')
+			->willReturn('1000-1000-max.png');
+
+		$previewFolder->method('getDirectoryListing')
+			->willReturn([$maxPreview]);
+
+		$previewFile = $this->createMock(ISimpleFile::class);
+
+		$previewFolder->method('getFile')
+			->with($this->equalTo('128-128.png'))
+			->willReturn($previewFile);
+
+		$result = $this->generator->getPreview($file, 100, 100);
+		$this->assertSame($previewFile, $result);
+	}
+
+	public function testGetNewPreview() {
+		$file = $this->createMock(File::class);
+		$file->method('getMimeType')
+			->willReturn('myMimeType');
+		$file->method('getId')
+			->willReturn(42);
+
+		$this->previewManager->method('isMimeSupported')
+			->with($this->equalTo('myMimeType'))
+			->willReturn(true);
+
+		$previewFolder = $this->createMock(ISimpleFolder::class);
+		$this->appData->method('getFolder')
+			->with($this->equalTo(42))
+			->willThrowException(new NotFoundException());
+
+		$this->appData->method('newFolder')
+			->with($this->equalTo(42))
+			->willReturn($previewFolder);
+
+		$this->config->method('getSystemValue')
+			->will($this->returnCallback(function($key, $defult) {
+				return $defult;
+			}));
+
+		$invalidProvider = $this->createMock(IProvider::class);
+		$validProvider = $this->createMock(IProvider::class);
+
+		$this->previewManager->method('getProviders')
+			->willReturn([
+				'/image\/png/' => ['wrongProvider'],
+				'/myMimeType/' => ['brokenProvider', 'invalidProvider', 'validProvider'],
+			]);
+
+		$this->helper->method('getProvider')
+			->will($this->returnCallback(function($provider) use ($invalidProvider, $validProvider) {
+				if ($provider === 'wrongProvider') {
+					$this->fail('Wrongprovider should not be constructed!');
+				} else if ($provider === 'brokenProvider') {
+					return false;
+				} else if ($provider === 'invalidProvider') {
+					return $invalidProvider;
+				} else if ($provider === 'validProvider') {
+					return $validProvider;
+				}
+				$this->fail('Unexpected provider requested');
+			}));
+
+		$image = $this->createMock(IImage::class);
+		$image->method('width')->willReturn(2048);
+		$image->method('height')->willReturn(2048);
+
+		$this->helper->method('getThumbnail')
+			->will($this->returnCallback(function ($provider, $file, $x, $y) use ($invalidProvider, $validProvider, $image) {
+				if ($provider === $validProvider) {
+					return $image;
+				} else {
+					return false;
+				}
+			}));
+
+		$image->method('data')
+			->willReturn('my data');
+
+		$maxPreview = $this->createMock(ISimpleFile::class);
+		$maxPreview->method('getName')->willReturn('2048-2048-max.png');
+
+		$previewFile = $this->createMock(ISimpleFile::class);
+
+		$previewFolder->method('getDirectoryListing')
+			->willReturn([]);
+		$previewFolder->method('newFile')
+			->will($this->returnCallback(function($filename) use ($maxPreview, $previewFile) {
+				if ($filename === '2048-2048-max.png') {
+					return $maxPreview;
+				} else if ($filename === '128-128.png') {
+					return $previewFile;
+				}
+				$this->fail('Unexpected file');
+			}));
+
+		$maxPreview->expects($this->once())
+			->method('putContent')
+			->with($this->equalTo('my data'));
+
+		$previewFolder->method('getFile')
+			->with($this->equalTo('128-128.png'))
+			->willThrowException(new NotFoundException());
+
+		$image = $this->createMock(IImage::class);
+		$this->helper->method('getImage')
+			->with($this->equalTo($maxPreview))
+			->willReturn($image);
+
+		$image->expects($this->once())
+			->method('resize')
+			->with(128);
+		$image->method('data')
+			->willReturn('my resized data');
+
+		$previewFile->expects($this->once())
+			->method('putContent')
+			->with('my resized data');
+
+		$result = $this->generator->getPreview($file, 100, 100);
+		$this->assertSame($previewFile, $result);
+	}
+
+	public function testInvalidMimeType() {
+		$this->expectException(NotFoundException::class);
+
+		$file = $this->createMock(File::class);
+
+		$this->previewManager->method('isMimeSupported')
+			->with('invalidType')
+			->willReturn(false);
+
+		$this->generator->getPreview($file, 0, 0, true, IPreview::MODE_COVER, 'invalidType');
+	}
+
+	public function testNoProvider() {
+		$file = $this->createMock(File::class);
+		$file->method('getMimeType')
+			->willReturn('myMimeType');
+		$file->method('getId')
+			->willReturn(42);
+
+		$this->previewManager->method('isMimeSupported')
+			->with($this->equalTo('myMimeType'))
+			->willReturn(true);
+
+		$previewFolder = $this->createMock(ISimpleFolder::class);
+		$this->appData->method('getFolder')
+			->with($this->equalTo(42))
+			->willReturn($previewFolder);
+
+		$previewFolder->method('getDirectoryListing')
+			->willReturn([]);
+
+		$this->previewManager->method('getProviders')
+			->willReturn([]);
+
+		$this->expectException(NotFoundException::class);
+		$this->generator->getPreview($file, 100, 100);
+	}
+
+	public function dataSize() {
+		return [
+			[1024, 2048, 512, 512, false, IPreview::MODE_FILL, 256, 512],
+			[1024, 2048, 512, 512, false, IPreview::MODE_COVER, 512, 1024],
+			[1024, 2048, 512, 512, true, IPreview::MODE_FILL, 512, 512],
+			[1024, 2048, 512, 512, true, IPreview::MODE_COVER, 512, 512],
+
+			[1024, 2048, -1, 512, false, IPreview::MODE_COVER, 256, 512],
+			[1024, 2048, 512, -1, false, IPreview::MODE_FILL, 512, 1024],
+
+			[1024, 2048, 250, 1100, true, IPreview::MODE_COVER, 256, 1126],
+			[1024, 1100, 250, 1100, true, IPreview::MODE_COVER, 250, 1100],
+
+			[1024, 2048, 4096, 2048, false, IPreview::MODE_FILL, 1024, 2048],
+			[1024, 2048, 4096, 2048, false, IPreview::MODE_COVER, 1024, 2048],
+
+
+			[2048, 1024, 512, 512, false, IPreview::MODE_FILL, 512, 256],
+			[2048, 1024, 512, 512, false, IPreview::MODE_COVER, 1024, 512],
+			[2048, 1024, 512, 512, true, IPreview::MODE_FILL, 512, 512],
+			[2048, 1024, 512, 512, true, IPreview::MODE_COVER, 512, 512],
+
+			[2048, 1024, -1, 512, false, IPreview::MODE_FILL, 1024, 512],
+			[2048, 1024, 512, -1, false, IPreview::MODE_COVER, 512, 256],
+
+			[2048, 1024, 4096, 1024, true, IPreview::MODE_FILL, 2048, 512],
+			[2048, 1024, 4096, 1024, true, IPreview::MODE_COVER, 2048, 512],
+		];
+	}
+
+	/**
+	 * @dataProvider dataSize
+	 *
+	 * @param int $maxX
+	 * @param int $maxY
+	 * @param int $reqX
+	 * @param int $reqY
+	 * @param bool $crop
+	 * @param string $mode
+	 * @param int $expectedX
+	 * @param int $expectedY
+	 */
+	public function testCorrectSize($maxX, $maxY, $reqX, $reqY, $crop, $mode, $expectedX, $expectedY) {
+		$file = $this->createMock(File::class);
+		$file->method('getMimeType')
+			->willReturn('myMimeType');
+		$file->method('getId')
+			->willReturn(42);
+
+		$this->previewManager->method('isMimeSupported')
+			->with($this->equalTo('myMimeType'))
+			->willReturn(true);
+
+		$previewFolder = $this->createMock(ISimpleFolder::class);
+		$this->appData->method('getFolder')
+			->with($this->equalTo(42))
+			->willReturn($previewFolder);
+
+		$maxPreview = $this->createMock(ISimpleFile::class);
+		$maxPreview->method('getName')
+			->willReturn($maxX . '-' . $maxY . '-max.png');
+
+		$previewFolder->method('getDirectoryListing')
+			->willReturn([$maxPreview]);
+
+		$filename = $expectedX . '-' . $expectedY;
+		if ($crop) {
+			$filename .= '-crop';
+		}
+		$filename .= '.png';
+		$previewFolder->method('getFile')
+			->with($this->equalTo($filename))
+			->willThrowException(new NotFoundException());
+
+		$image = $this->createMock(IImage::class);
+		$this->helper->method('getImage')
+			->with($this->equalTo($maxPreview))
+			->willReturn($image);
+		$image->method('height')->willReturn($maxY);
+		$image->method('width')->willReturn($maxX);
+
+		$preview = $this->createMock(ISimpleFile::class);
+		$previewFolder->method('newFile')
+			->with($this->equalTo($filename))
+			->willReturn($preview);
+
+		$result = $this->generator->getPreview($file, $reqX, $reqY, $crop, $mode);
+		$this->assertSame($preview, $result);
+	}
+}