Fixes read_preference

Fixes mongoengine/mongoengine#10

tests/replicaset_connection.py

@@ -0,0 +1,28 @@
+import unittest
+import pymongo
+from pymongo import ReadPreference
+
+import mongoengine
+from mongoengine import *
+from mongoengine.connection import get_db, get_connection, ConnectionError
+
+
+class ConnectionTest(unittest.TestCase):
+
+    def tearDown(self):
+        mongoengine.connection._connection_settings = {}
+        mongoengine.connection._connections = {}
+        mongoengine.connection._dbs = {}
+
+    def test_replicaset_uri_passes_read_preference(self):
+        """Requires a replica set called "rs" on port 27017
+        """
+        try:
+            conn = connect(db='mongoenginetest', host="mongodb://localhost/mongoenginetest?replicaSet=rs", read_preference=ReadPreference.SECONDARY_ONLY)
+        except ConnectionError, e:
+            return
+
+        self.assertEquals(conn.read_preference, ReadPreference.SECONDARY_ONLY)
+
+if __name__ == '__main__':
+    unittest.main()