Make tests compatible with pymongo >= 4.14

mongodb/mongo-python-driver#2413 caused some
test regressions here.  This isn't currently a problem for the upstream
test suite since it pins pymongo==4.10.1 via kombu, but we're running
into it in Debian where we've already upgraded pymongo for other
reasons.  kombu already tried to upgrade pymongo but had to revert due
to these test regressions (see celery/kombu#2384
and celery#9938).

One of the test fixes (relating to `mongodb_backend_settings`)
illustrates an incompatibility where I couldn't figure out a reasonable
way to avoid passing it through to Celery users, so I added a note to
the documentation about it.  It may also be worth including a brief
mention of it in the release notes.  Using the canonical case for the
option in question should work with both old and new versions of
pymongo.

Author: cjwatson

docs/userguide/configuration.rst

@@ -1208,6 +1208,12 @@ This is a dict supporting the following keys:
     constructor.  See the :mod:`pymongo` docs to see a list of arguments
     supported.
 
+.. note::
+
+    With pymongo>=4.14, options are case-sensitive when they were previously
+    case-insensitive.  See :class:`~pymongo.mongo_client.MongoClient` to
+    determine the correct case.
+
 .. _example-mongodb-result-config:
 
 Example configuration

t/unit/backends/test_mongodb.py

@@ -130,17 +130,21 @@ def test_init_with_settings(self):
                'celerydatabase?replicaSet=rs0')
         mb = MongoBackend(app=self.app, url=uri)
         assert mb.mongo_host == MONGODB_BACKEND_HOST
-        assert mb.options == dict(
-            mb._prepare_client_options(),
-            replicaset='rs0',
-        )
+        if 'replicaSet' in mb.options:  # pragma: no cover  # pymongo >= 4.14
+            replicaset_option = 'replicaSet'
+        else:  # pragma: no cover  # pymongo < 4.14
+            replicaset_option = 'replicaset'
+        assert mb.options == {
+            **mb._prepare_client_options(),
+            replicaset_option: 'rs0',
+        }
         assert mb.user == CELERY_USER
         assert mb.password == CELERY_PASSWORD
         assert mb.database_name == CELERY_DATABASE
 
         # same uri, change some parameters in backend settings
         self.app.conf.mongodb_backend_settings = {
-            'replicaset': 'rs1',
+            replicaset_option: 'rs1',
             'user': 'backenduser',
             'database': 'another_db',
             'options': {
@@ -149,11 +153,11 @@ def test_init_with_settings(self):
         }
         mb = MongoBackend(app=self.app, url=uri)
         assert mb.mongo_host == MONGODB_BACKEND_HOST
-        assert mb.options == dict(
-            mb._prepare_client_options(),
-            replicaset='rs1',
-            socketKeepAlive=True,
-        )
+        assert mb.options == {
+            **mb._prepare_client_options(),
+            replicaset_option: 'rs1',
+            'socketKeepAlive': True,
+        }
         assert mb.user == 'backenduser'
         assert mb.password == CELERY_PASSWORD
         assert mb.database_name == 'another_db'
@@ -222,11 +226,15 @@ def test_init_mongodb_dnspython2_pymongo4_seedlist(self):
 
         with patch('dns.resolver.resolve', side_effect=resolver):
             mb = self.perform_seedlist_assertions()
-            assert mb.options == dict(
-                mb._prepare_client_options(),
-                replicaset='rs0',
-                tls=True
-            )
+            if 'replicaSet' in mb.options:  # pragma: no cover  # pymongo >= 4.14
+                replicaset_option = 'replicaSet'
+            else:  # pragma: no cover  # pymongo < 4.14
+                replicaset_option = 'replicaset'
+            assert mb.options == {
+                **mb._prepare_client_options(),
+                replicaset_option: 'rs0',
+                'tls': True,
+            }
 
     def perform_seedlist_assertions(self):
         mb = MongoBackend(app=self.app, url=MONGODB_SEEDLIST_URI)
@@ -299,12 +307,15 @@ def test_get_connection_with_authmechanism(self):
             mb = MongoBackend(app=self.app, url=uri)
             mock_Connection.return_value = sentinel.connection
             connection = mb._get_connection()
+            if 'authMechanism' in mb.options:  # pragma: no cover  # pymongo >= 4.14
+                authmechanism_option = 'authMechanism'
+            else:  # pragma: no cover  # pymongo < 4.14
+                authmechanism_option = 'authmechanism'
             mock_Connection.assert_called_once_with(
                 host=['localhost:27017'],
                 username=CELERY_USER,
                 password=CELERY_PASSWORD,
-                authmechanism='SCRAM-SHA-256',
-                **mb._prepare_client_options()
+                **{**mb._prepare_client_options(), authmechanism_option: 'SCRAM-SHA-256'}
             )
             assert sentinel.connection == connection
 
@@ -319,10 +330,13 @@ def test_get_connection_with_authmechanism_no_username(self):
                 'SCRAM-SHA-256 requires a username.')
             with pytest.raises(ConfigurationError):
                 mb._get_connection()
+            if 'authMechanism' in mb.options:  # pragma: no cover  # pymongo >= 4.14
+                authmechanism_option = 'authMechanism'
+            else:  # pragma: no cover  # pymongo < 4.14
+                authmechanism_option = 'authmechanism'
             mock_Connection.assert_called_once_with(
                 host=['localhost:27017'],
-                authmechanism='SCRAM-SHA-256',
-                **mb._prepare_client_options()
+                **{**mb._prepare_client_options(), authmechanism_option: 'SCRAM-SHA-256'}
             )
 
     @patch('celery.backends.mongodb.MongoBackend._get_connection')