diff --git a/classes/backends/ComicPressBackendFilesystem.inc b/classes/backends/ComicPressBackendFilesystem.inc
index 720286f..abd632f 100644
--- a/classes/backends/ComicPressBackendFilesystem.inc
+++ b/classes/backends/ComicPressBackendFilesystem.inc
@@ -12,10 +12,12 @@ class ComicPressBackendFilesystem extends ComicPressBackend {
 		$this->source_name = __('Filesystem', 'comicpress');
 	}
 
+	function _getimagesize($file) { return getimagesize($file); }
+
 	function dims($size = null) {
 		$dims = array();
 
-		if ($result = getimagesize($this->files_by_type[$this->ensure_type($size)])) {
+		if ($result = $this->_getimagesize($this->files_by_type[$this->ensure_type($size)])) {
 			$dims = array_combine(array('width', 'height'), array_slice($result, 0, 2));
 		}
 
diff --git a/test/backends/ComicPressBackendFilesystemTest.php b/test/backends/ComicPressBackendFilesystemTest.php
index 2aee51b..17c1eaf 100644
--- a/test/backends/ComicPressBackendFilesystemTest.php
+++ b/test/backends/ComicPressBackendFilesystemTest.php
@@ -15,5 +15,40 @@ class ComicPressBackendFilesystemTest extends PHPUnit_Framework_TestCase {
 		vfsStreamWrapper::setRoot(new vfsStreamDirectory('root'));
 	}
 
-	function testSomething() {}
+	function providerTestDims() {
+		return array(
+			array(false, array()),
+			array(
+				array(
+					200, 100, 300
+				),
+				array(
+					'width' => 200,
+					'height' => 100
+				)
+			)
+		);
+	}
+
+	/**
+	 * @dataProvider providerTestDims
+	 */
+	function testDims($getimagesize_return, $expected_result) {
+		$fs = $this->getMock('ComicPressBackendFilesystem', array('_getimagesize', 'ensure_type'));
+		$fs->expects($this->once())->method('ensure_type')->with('type')->will($this->returnValue('newtype'));
+		$fs->expects($this->once())->method('_getimagesize')->with('file')->will($this->returnValue($getimagesize_return));
+
+		$fs->files_by_type = array('newtype' => 'file');
+
+		$this->assertEquals($expected_result, $fs->dims('type'));
+	}
+
+	function testUrl() {
+		$fs = $this->getMock('ComicPressBackendFilesystem', array('ensure_type'));
+		$fs->expects($this->once())->method('ensure_type')->with('type')->will($this->returnValue('newtype'));
+
+		$fs->file_urls_by_type = array('newtype' => 'url');
+
+		$this->assertEquals('url', $fs->url('type'));
+	}
 }