--- a/tests/test_viewer.py	Mon Sep 18 15:45:42 2017 +0800
+++ b/tests/test_viewer.py	Mon Sep 18 16:54:55 2017 +0800
@@ -181,8 +181,7 @@
         root = ElementTree.fromstring(response.body)
         ns = {'svg': 'http://www.w3.org/2000/svg'}
         assert root.tag == '{http://www.w3.org/2000/svg}svg'
-        assert 'height' in root.attrib
-        assert root.attrib['height'] == '20'
+        assert root.attrib.get('height') == '20'
         text = [el.text for el in root.findall('./svg:g/svg:text', ns)]
         assert text[::2] == ['lint', '1 error', '1 warning']