diff --git a/IPython/nbconvert/filters/tests/test_strings.py b/IPython/nbconvert/filters/tests/test_strings.py
index d4e0527..f93749c 100644
--- a/IPython/nbconvert/filters/tests/test_strings.py
+++ b/IPython/nbconvert/filters/tests/test_strings.py
@@ -88,12 +88,19 @@ class TestStrings(TestsBase):
('test="/files"', 'test="/files"'),
('My files are in `files/`', 'My files are in `files/`'),
('files/test.html', 'files/test.html'),
+ ('files/test.html', 'files/test.html'),
+ ("files/test.html", "files/test.html"),
+ ('', ''),
+ ('', ''),
('hello![caption]', 'hello![caption]'),
('hello![caption](/url/location.gif)', 'hello![caption](/url/location.gif)'),
('hello![caption](url/location.gif)', 'hello![caption](url/location.gif)'),
('hello![caption](url/location.gif)', 'hello![caption](url/location.gif)'),
('hello![caption](files/url/location.gif)', 'hello![caption](url/location.gif)'),
- ('hello![caption](/files/url/location.gif)', 'hello![caption](url/location.gif)'),]
+ ('hello![caption](/files/url/location.gif)', 'hello![caption](url/location.gif)'),
+ ('hello [text](/files/url/location.gif)', 'hello [text](url/location.gif)'),
+ ('hello [text space](files/url/location.gif)', 'hello [text space](url/location.gif)'),
+ ]
for test in tests:
self._try_files_prefix(test[0], test[1])