fix test suite

is_hidden expects the file to actually exist, so I've rearranged the
logic such that is_hidden is called only after it's clear that the file
exists.

IPython/html/services/notebooks/filenbmanager.py

@@ -180,9 +180,10 b' class FileNotebookManager(NotebookManager):'
         """List the directories for a given API style path."""
         path = path.strip('/')
         os_path = self._get_os_path('', path)
-        if is_hidden(os_path, self.notebook_dir):
+        if not os.path.isdir(os_path):
+            raise web.HTTPError(404, u'directory does not exist: %r' % os_path)
+        elif is_hidden(os_path, self.notebook_dir):
             self.log.info("Refusing to serve hidden directory, via 404 Error")
-        if not os.path.isdir(os_path) or is_hidden(os_path, self.notebook_dir):
             raise web.HTTPError(404, u'directory does not exist: %r' % os_path)
         dir_names = os.listdir(os_path)
         dirs = []

IPython/html/tree/handlers.py

@@ -62,11 +62,12 b' class TreeHandler(IPythonHandler):'
             self.log.debug("Redirecting %s to %s", self.request.path, url)
             self.redirect(url)
         else:
-            if nbm.is_hidden(path):
-                self.log.info("Refusing to serve hidden directory, via 404 Error")
-            if not nbm.path_exists(path=path) or nbm.is_hidden(path):
+            if not nbm.path_exists(path=path):
                 # Directory is hidden or does not exist.
                 raise web.HTTPError(404)
+            elif nbm.is_hidden(path):
+                self.log.info("Refusing to serve hidden directory, via 404 Error")
+                raise web.HTTPError(404)
             breadcrumbs = self.generate_breadcrumbs(path)
             page_title = self.generate_page_title(path)
             self.write(self.render_template('tree.html',