PYTHON-1911 Implement missing changeStream prose tests

Author: prashantmital

test/__init__.py

@@ -29,6 +29,7 @@
 except ImportError:
     HAVE_IPADDRESS = False
 
+from contextlib import contextmanager
 from functools import wraps
 from unittest import SkipTest
 
@@ -585,6 +586,13 @@ def require_test_commands(self, func):
                              "Test commands must be enabled",
                              func=func)
 
+    def require_failCommand_fail_point(self, func):
+        """Run a test only if the server supports the failCommand fail
+        point."""
+        return self._require(lambda: self.supports_failCommand_fail_point,
+                             "failCommand fail point must be supported",
+                             func=func)
+
     def require_ssl(self, func):
         """Run a test only if the client can connect over SSL."""
         return self._require(lambda: self.ssl,
@@ -656,6 +664,17 @@ def supports_getpreverror(self):
         """Does the connected server support getpreverror?"""
         return not (self.version.at_least(4, 1, 0) or self.is_mongos)
 
+    @property
+    def supports_failCommand_fail_point(self):
+        """Does the server support the failCommand fail point?"""
+        if self.is_mongos:
+            return (self.version.at_least(4, 1, 5) and
+                    self.test_commands_enabled)
+        else:
+            return (self.version.at_least(4, 0) and
+                    self.test_commands_enabled)
+
+
     @property
     def requires_hint_with_min_max_queries(self):
         """Does the server require a hint with min/max queries."""
@@ -713,6 +732,17 @@ def setUpClass(cls):
         else:
             cls.credentials = {}
 
+    @contextmanager
+    def fail_point(self, command_args):
+        cmd_on = SON([('configureFailPoint', 'failCommand')])
+        cmd_on.update(command_args)
+        self.client.admin.command(cmd_on)
+        try:
+            yield
+        finally:
+            cmd_off = {'configureFailPoint': cmd_on['configureFailPoint'],
+                       'mode': 'off'}
+            self.client.admin.command(cmd_off)
 
 # Use assertRaisesRegex if available, otherwise use Python 2.7's
 # deprecated assertRaisesRegexp, with a 'p'.

test/test_change_stream.py

@@ -23,6 +23,7 @@
 import time
 import uuid
 
+from contextlib import contextmanager
 from itertools import product
 
 sys.path[0:0] = ['']
@@ -535,26 +536,65 @@ def test_resume_on_error(self):
             self.kill_change_stream_cursor(change_stream)
             self.insert_one_and_check(change_stream, {'_id': 2})
 
+    # Prose test no. 4
+    @client_context.require_failCommand_fail_point
+    def test_no_resume_attempt_if_aggregate_command_fails(self):
+        # Set non-retryable error on aggregate command.
+        fail_point = {'mode': {'times': 1},
+                      'data': {'errorCode': 2, 'failCommands': ['aggregate']}}
+        client, listener = self._client_with_listener("aggregate", "getMore")
+        with self.fail_point(fail_point):
+            try:
+                _ = self.change_stream_with_client(client)
+            except OperationFailure:
+                pass
+
+        # Driver should have attempted aggregate command only once.
+        self.assertEqual(len(listener.results['started']), 1)
+        self.assertEqual(listener.results['started'][0].command_name,
+                         'aggregate')
+
     # Prose test no. 5
     def test_does_not_resume_fatal_errors(self):
         """ChangeStream will not attempt to resume fatal server errors."""
-        for code in _NON_RESUMABLE_GETMORE_ERRORS:
-            with self.change_stream() as change_stream:
-                self.watched_collection().insert_one({})
-
+        if client_context.supports_failCommand_fail_point:
+            # failCommand does not support returning no errorCode.
+            TEST_ERROR_CODES = _NON_RESUMABLE_GETMORE_ERRORS - {None}
+            @contextmanager
+            def generate_error(change_stream, code):
+                fail_point = {'mode': {'times': 1}, 'data': {
+                    'errorCode': code, 'failCommands': ['getMore']}}
+                with self.fail_point(fail_point):
+                    yield
+        else:
+            TEST_ERROR_CODES = _NON_RESUMABLE_GETMORE_ERRORS
+            @contextmanager
+            def generate_error(change_stream, code):
                 def mock_try_next(*args, **kwargs):
                     change_stream._cursor.close()
                     raise OperationFailure('Mock server error', code=code)
 
                 original_try_next = change_stream._cursor._try_next
                 change_stream._cursor._try_next = mock_try_next
+                try:
+                    yield
+                finally:
+                    change_stream._cursor._try_next = original_try_next
 
-                with self.assertRaises(OperationFailure):
-                    next(change_stream)
-                change_stream._cursor._try_next = original_try_next
+        for code in TEST_ERROR_CODES:
+            with self.change_stream() as change_stream:
+                self.watched_collection().insert_one({})
+                with generate_error(change_stream, code):
+                    with self.assertRaises(OperationFailure):
+                        next(change_stream)
                 with self.assertRaises(StopIteration):
                     next(change_stream)
 
+    # Prose test no. 6 - SKIPPED
+    # readPreference is not configurable using the watch() helpers so we can
+    # skip this test. Also, PyMongo performs server selection for each
+    # operation which ensure compliance with this prose test.
+
     # Prose test no. 7
     def test_initial_empty_batch(self):
         with self.change_stream() as change_stream:
@@ -603,6 +643,9 @@ def test_start_at_operation_time_caching(self):
             "startAtOperationTime"), optime, str([k.command for k in
                                                   listener.results['started']]))
 
+    # Prose test no. 10 - SKIPPED
+    # This test is identical to prose test no. 3.
+
     # Prose test no. 11
     @client_context.require_version_min(4, 0, 7)
     def test_resumetoken_empty_batch(self):