diff --git a/tests/storage/__init__.py b/tests/storage/__init__.py
index fc570bc..154143d 100644
--- a/tests/storage/__init__.py
+++ b/tests/storage/__init__.py
@@ -108,4 +108,6 @@ class StorageTests(object):
 
     def test_collection_arg(self):
         s = self.storage_class(**self.get_storage_args(collection='asd'))
-        assert s.collection == 'asd'
+        # Can't do stronger assertion because of radicale, which needs a
+        # fileextension to guess the collection type.
+        assert 'asd' in s.collection
diff --git a/tests/storage/dav/__init__.py b/tests/storage/dav/__init__.py
index 22b2e6c..2c7d45c 100644
--- a/tests/storage/dav/__init__.py
+++ b/tests/storage/dav/__init__.py
@@ -139,8 +139,10 @@ class DavStorageTests(StorageTests):
         self.patcher = p = mock.patch('requests.Session.request', new=x)
         p.start()
 
-    def get_storage_args(self, collection=None):
+    def get_storage_args(self, collection='test'):
         url = 'http://127.0.0.1/bob/'
+        if collection is not None:
+            collection += self.storage_class.fileext
         return {'url': url, 'collection': collection}
 
     def teardown_method(self, method):