Make test_collection_arg more generic

tests/storage/__init__.py

@@ -208,11 +208,15 @@ class StorageTests(object):
 
         assert 'collection argument must not be given' in str(excinfo.value)
 
-    def test_collection_arg(self, requires_collections, get_storage_args):
-        s = self.storage_class(**get_storage_args(collection='test2'))
-        # Can't do stronger assertion because of radicale, which needs a
-        # fileextension to guess the collection type.
-        assert 'test2' in s.collection
+    def test_collection_arg(self, get_storage_args):
+        if self.supports_collections:
+            s = self.storage_class(**get_storage_args(collection='test2'))
+            # Can't do stronger assertion because of radicale, which needs a
+            # fileextension to guess the collection type.
+            assert 'test2' in s.collection
+        else:
+            with pytest.raises(ValueError):
+                self.storage_class(**get_storage_args(), collection='ayy')
 
     def test_case_sensitive_uids(self, s, get_item):
         if s.storage_name == 'filesystem':

tests/storage/test_http_with_singlefile.py

@@ -17,6 +17,9 @@ class CombinedStorage(Storage):
     _repr_attributes = ('url', 'path')
 
     def __init__(self, url, path, **kwargs):
+        if kwargs.get('collection', None) is not None:
+            raise ValueError()
+
         super(CombinedStorage, self).__init__(**kwargs)
         self.url = url
         self.path = path

tests/storage/test_singlefile.py

@@ -23,7 +23,3 @@ class TestSingleFileStorage(StorageTests):
             kwargs.update(path=self._path)
             return kwargs
         return inner
-
-    def test_collection_arg(self, tmpdir):
-        with pytest.raises(ValueError):
-            self.storage_class(str(tmpdir.join('foo.ics')), collection='ha')