FIX: explicitly state read and write concern in causal consistency examples (mongodb#374)

PYTHON-1623 Causal Consistency Examples for the Manual

Author: prashantmital

test/test_examples.py

@@ -1128,7 +1128,9 @@ def test_causal_consistency(self):
  # Start Causal Consistency Example 1
  with client.start_session(causal_consistency=True) as s1:
  current_date = datetime.datetime.today()
- items = client.get_database('test').items
+ items = client.get_database(
+ 'test', read_concern=ReadConcern('majority'),
+ write_concern=WriteConcern('majority', wtimeout=1000)).items
  items.update_one(
  {'sku': "111", 'end': None},
  {'$set': {'end': current_date}}, session=s1)
@@ -1143,7 +1145,9 @@ def test_causal_consistency(self):
  s2.advance_operation_time(s1.operation_time)
 
  items = client.get_database(
- 'test', read_preference=ReadPreference.SECONDARY).items
+ 'test', read_preference=ReadPreference.SECONDARY,
+ read_concern=ReadConcern('majority'),
+ write_concern=WriteConcern('majority', wtimeout=1000)).items
  for item in items.find({'end': None}, session=s2):
  print(item)
  # End Causal Consistency Example 2