Load the CollectionWrapper from a factory method

This allows a class implementing CollectionWrapper's interface to be
added from config

tests/test_collection_wrappers.py

@@ -0,0 +1,47 @@
+# -*- coding: utf-8 -*-
+
+import os
+import unittest
+import configparser
+
+from ankisyncd.collection import CollectionWrapper
+from ankisyncd.collection import get_collection_wrapper
+
+import helpers.server_utils
+
+class FakeCollectionWrapper(CollectionWrapper):
+    def __init__(self, config, path, setup_new_collection=None):
+        self. _CollectionWrapper__col = None
+        pass
+
+class BadCollectionWrapper:
+    pass
+
+class CollectionWrapperFactoryTest(unittest.TestCase):
+    def test_get_collection_wrapper(self):
+        # Get absolute path to development ini file.
+        script_dir = os.path.dirname(os.path.realpath(__file__))
+        ini_file_path = os.path.join(script_dir,
+                                     "assets",
+                                     "test.conf")
+
+        # Create temporary files and dirs the server will use.
+        server_paths = helpers.server_utils.create_server_paths()
+
+        config = configparser.ConfigParser()
+        config.read(ini_file_path)
+        path = os.path.realpath('fake/collection.anki2')
+
+        # Use custom files and dirs in settings. Should be CollectionWrapper
+        config['sync_app'].update(server_paths)
+        self.assertTrue(type(get_collection_wrapper(config['sync_app'], path) == CollectionWrapper))
+
+        # A conf-specified CollectionWrapper is loaded
+        config.set("sync_app", "collection_wrapper", 'test_collection_wrappers.FakeCollectionWrapper')
+        self.assertTrue(type(get_collection_wrapper(config['sync_app'], path)) == FakeCollectionWrapper)
+
+        # Should fail at load time if the class doesn't inherit from CollectionWrapper
+        config.set("sync_app", "collection_wrapper", 'test_collection_wrappers.BadCollectionWrapper')
+        with self.assertRaises(TypeError):
+            pm = get_collection_wrapper(config['sync_app'], path)
+