Convert test to DDT and test for primary, nearest modes.

common/lib/xmodule/xmodule/tests/test_mongo_utils.py

-"""Tests for methods defined in mongo_utils.py"""
+"""
+Tests for methods defined in mongo_utils.py
+"""
+import ddt
 import os
 from unittest import TestCase
 from uuid import uuid4
@@ -10,19 +13,26 @@ from django.conf import settings
 from xmodule.mongo_utils import connect_to_mongodb
 
 
+@ddt.ddt
 class MongoUtilsTests(TestCase):
     """
     Tests for methods exposed in mongo_utils
     """
-    def test_connect_to_mongo_read_preference(self):
+    @ddt.data(
+        ('PRIMARY', 'primary', ReadPreference.PRIMARY),
+        ('SECONDARY_PREFERRED', 'secondaryPreferred', ReadPreference.SECONDARY_PREFERRED),
+        ('NEAREST', 'nearest', ReadPreference.NEAREST),
+    )
+    @ddt.unpack
+    def test_connect_to_mongo_read_preference(self, enum_name, mongos_name, expected_read_preference):
         """
         Test that read_preference parameter gets converted to a valid pymongo read preference.
         """
         host = 'edx.devstack.mongo' if 'BOK_CHOY_HOSTNAME' in os.environ else 'localhost'
         db = 'test_read_preference_%s' % uuid4().hex
         # Support for read_preference given in constant name form (ie. PRIMARY, SECONDARY_PREFERRED)
-        connection = connect_to_mongodb(db, host, read_preference='SECONDARY_PREFERRED')
-        self.assertEqual(connection.client.read_preference, ReadPreference.SECONDARY_PREFERRED)
+        connection = connect_to_mongodb(db, host, read_preference=enum_name)
+        self.assertEqual(connection.client.read_preference, expected_read_preference)
         # Support for read_preference given as mongos name.
-        connection = connect_to_mongodb(db, host, read_preference='secondaryPreferred')
-        self.assertEqual(connection.client.read_preference, ReadPreference.SECONDARY_PREFERRED)
+        connection = connect_to_mongodb(db, host, read_preference=mongos_name)
+        self.assertEqual(connection.client.read_preference, expected_read_preference)