PYTHON-1793 Use _id:1 in countDocuments to follow the updated CRUD spec

Author: ShaneHarvey

pymongo/collection.py

@@ -1676,7 +1676,7 @@ def count_documents(self, filter, session=None, **kwargs):
             pipeline.append({'$skip': kwargs.pop('skip')})
         if 'limit' in kwargs:
             pipeline.append({'$limit': kwargs.pop('limit')})
-        pipeline.append({'$group': {'_id': None, 'n': {'$sum': 1}}})
+        pipeline.append({'$group': {'_id': 1, 'n': {'$sum': 1}}})
         cmd = SON([('aggregate', self.__name),
                    ('pipeline', pipeline),
                    ('cursor', {})])

test/transactions/mongos-recovery-token.json

@@ -265,7 +265,7 @@
       "description": "commitTransaction retry fails on new mongos",
       "useMultipleMongoses": true,
       "clientOptions": {
-        "heartbeatFrequencyMS": 5000
+        "heartbeatFrequencyMS": 30000
       },
       "operations": [
         {

test/transactions/pin-mongos.json

@@ -1068,7 +1068,7 @@
       "description": "unpin after transient error within a transaction and commit",
       "useMultipleMongoses": true,
       "clientOptions": {
-        "heartbeatFrequencyMS": 5000
+        "heartbeatFrequencyMS": 30000
       },
       "operations": [
         {

test/transactions/read-concern.json

@@ -90,7 +90,7 @@
                 },
                 {
                   "$group": {
-                    "_id": null,
+                    "_id": 1,
                     "n": {
                       "$sum": 1
                     }
@@ -126,7 +126,7 @@
                 },
                 {
                   "$group": {
-                    "_id": null,
+                    "_id": 1,
                     "n": {
                       "$sum": 1
                     }
@@ -900,7 +900,7 @@
                 },
                 {
                   "$group": {
-                    "_id": null,
+                    "_id": 1,
                     "n": {
                       "$sum": 1
                     }
@@ -934,7 +934,7 @@
                 },
                 {
                   "$group": {
-                    "_id": null,
+                    "_id": 1,
                     "n": {
                       "$sum": 1
                     }