Copilot review

Author: aclark4life

test/test_message.py

@@ -24,7 +24,7 @@
 
 from test import unittest
 
-from bson import CodecOptions
+from bson import CodecOptions, encode
 from pymongo.compression_support import ZlibContext
 from pymongo.errors import DocumentTooLarge, OperationFailure
 from pymongo.message import (
@@ -98,6 +98,11 @@ def test_client_bulk_exception_includes_code(self):
 
 
 class TestConvertWriteResult(unittest.TestCase):
+    """Tests for _convert_write_result.
+
+    In the update command spec, `q` is the query/filter and `u` is the update document.
+    """
+
     def test_insert_basic(self):
         cmd = {"documents": [{"_id": 1}, {"_id": 2}]}
         result = _convert_write_result("insert", cmd, {"n": 0})
@@ -116,12 +121,12 @@ def test_update_with_upserted_id(self):
         self.assertIn("upserted", result)
         self.assertEqual(result["upserted"][0]["_id"], 42)
 
-    def test_update_implicit_upsert_from_updatedExisting_false(self):
-        cmd = {"updates": [{"q": {"_id": 99}, "u": {"$set": {"x": 1}}}]}
-        result = _convert_write_result(
-            "update", cmd, {"n": 1, "updatedExisting": False, "upserted": None}
-        )
-        self.assertIn("upserted", result)
+    def test_update_upsert_id_precedence(self):
+        # When _id is in both the update document and the query spec,
+        # the update document's _id wins.
+        cmd = {"updates": [{"q": {"_id": 99}, "u": {"_id": 42}}]}
+        result = _convert_write_result("update", cmd, {"n": 1, "updatedExisting": False})
+        self.assertEqual(result["upserted"][0]["_id"], 42)
 
     def test_update_upsert_no_upserted_id_from_query(self):
         cmd = {"updates": [{"q": {"_id": 77}, "u": {"$set": {"x": 1}}}]}
@@ -174,10 +179,11 @@ def test_max_doc_size_zero_without_docs(self):
         _, _, _, max_doc_size = _op_msg(0, {"ping": 1}, "testdb", None, _OPTS)
         self.assertEqual(max_doc_size, 0)
 
-    def test_max_doc_size_nonzero_with_docs(self):
-        cmd: dict = {"insert": "col", "documents": [{"_id": 1, "x": 2}, {"_id": 3, "x": 4}]}
+    def test_max_doc_size_matches_largest_encoded_doc(self):
+        docs = [{"_id": 1, "x": 2}, {"_id": 3, "x": 4}]
+        cmd: dict = {"insert": "col", "documents": docs}
         _, _, _, max_doc_size = _op_msg(0, cmd, "testdb", None, _OPTS)
-        self.assertGreater(max_doc_size, 0)
+        self.assertEqual(max_doc_size, max(len(encode(d)) for d in docs))
 
     def test_read_preference_added_for_non_primary(self):
         cmd: dict = {"find": "col"}
@@ -203,10 +209,6 @@ def test_command_with_documents_field_is_restored(self):
 
 
 class TestQuery(unittest.TestCase):
-    def test_basic(self):
-        _, max_bson_size = _query_impl(0, "db.col", 0, 0, {"x": 1}, None, _OPTS)
-        self.assertGreater(max_bson_size, 0)
-
     def test_uncompressed_op_code(self):
         _rid, msg, _mbs = _query_uncompressed(0, "db.col", 0, 0, {}, None, _OPTS)
         op_code = struct.unpack("<i", msg[12:16])[0]
@@ -252,7 +254,7 @@ def test_basic(self):
 
     def test_with_projection(self):
         cmd = _gen_find_command("col", {}, {"x": 1}, 0, 0, None, None, ReadConcern())
-        self.assertIn("projection", cmd)
+        self.assertEqual(cmd["projection"], {"x": 1})
 
     def test_with_skip(self):
         cmd = _gen_find_command("col", {}, None, 5, 0, None, None, ReadConcern())
@@ -279,7 +281,7 @@ def test_batch_size_not_adjusted_when_different(self):
 
     def test_read_concern_level_included(self):
         cmd = _gen_find_command("col", {}, None, 0, 0, None, None, ReadConcern("majority"))
-        self.assertIn("readConcern", cmd)
+        self.assertEqual(cmd["readConcern"], {"level": "majority"})
 
     def test_query_with_dollar_query_modifier(self):
         spec = {"$query": {"x": 1}, "$orderby": {"x": 1}}