Add unit tests for max_concurrency optional behavior

Co-authored-by: bambriz <[email protected]>

Author: Copilot

sdk/cosmos/azure-cosmos/tests/test_max_concurrency.py

@@ -0,0 +1,54 @@
+# -*- coding: utf-8 -*-
+# The MIT License (MIT)
+# Copyright (c) Microsoft Corporation. All rights reserved.
+import unittest
+from concurrent.futures import ThreadPoolExecutor
+from unittest.mock import Mock
+from azure.cosmos._read_items_helper import ReadItemsHelperSync
+
+
+class TestMaxConcurrency(unittest.TestCase):
+    """Unit tests for max_concurrency parameter behavior."""
+
+    def test_max_concurrency_none_uses_default(self):
+        """Test that max_concurrency=None uses ThreadPoolExecutor's default."""
+        # Mock client connection
+        mock_client = Mock()
+        mock_client._routing_map_provider = Mock()
+        mock_client._routing_map_provider.get_overlapping_ranges = Mock(return_value=[])
+        
+        # Create helper with max_concurrency=None
+        helper = ReadItemsHelperSync(
+            client=mock_client,
+            collection_link="/dbs/test/colls/test",
+            items=[],
+            options={},
+            partition_key_definition={"paths": ["/id"], "kind": "Hash"},
+            max_concurrency=None
+        )
+        
+        # Verify that max_concurrency is None
+        self.assertIsNone(helper.max_concurrency)
+        
+    def test_max_concurrency_value_is_preserved(self):
+        """Test that explicit max_concurrency value is preserved."""
+        # Mock client connection
+        mock_client = Mock()
+        mock_client._routing_map_provider = Mock()
+        
+        # Create helper with explicit max_concurrency
+        helper = ReadItemsHelperSync(
+            client=mock_client,
+            collection_link="/dbs/test/colls/test",
+            items=[],
+            options={},
+            partition_key_definition={"paths": ["/id"], "kind": "Hash"},
+            max_concurrency=5
+        )
+        
+        # Verify that max_concurrency is set correctly
+        self.assertEqual(helper.max_concurrency, 5)
+
+
+if __name__ == '__main__':
+    unittest.main()