feat: Spanner Mock Server

[bhatt4982]

Add Spanner Mock Server to Python Monorepo.

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Fixes#16040 🦕

[gemini-code-assist]

Summary of Changes

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This pull request delivers a crucial tool for Python developers working with Google Cloud Spanner: an in-memory mock server. This server facilitates local development and testing by mimicking the behavior of a real Spanner instance, allowing for faster feedback cycles and more robust automated tests. It abstracts away the complexities of interacting with a live service, making it easier to simulate various scenarios and edge cases during development.

Highlights

• New Spanner Mock Server Library: Introduced a new Python library, google-cloud-spanner-mockserver, to provide an in-memory mock server for Google Cloud Spanner. This enables developers to test Spanner applications without requiring a live Spanner instance.
• gRPC Service Mocking: Implemented mock servicers for both the Spanner API and the Spanner Database Admin API, allowing for the simulation of various gRPC calls and responses.
• Test Utilities and Integration: Provided a MockServerTestBase class to simplify the setup and teardown of the mock server in unit and integration tests, along with helper functions for mocking SQL query results and errors.
• Automated gRPC Code Generation: Configured Nox sessions to automatically generate gRPC client and server code from Googleapis protobuf definitions, including a post-processing step to ensure compatibility with google-cloud-spanner's proto-plus types.

Changelog

• packages/google-cloud-spanner-mockserver/.gitignore
  • Added standard Python and IDE-specific ignore patterns.
• packages/google-cloud-spanner-mockserver/LICENSE
  • Added the Apache License, Version 2.0.
• packages/google-cloud-spanner-mockserver/README.md
  • Added comprehensive documentation covering installation, usage examples, and API reference for the mock server.
• packages/google-cloud-spanner-mockserver/noxfile.py
  • Added Nox sessions for code formatting (isort, black), linting (flake8), unit testing, integration testing, gRPC code generation, and package building/installation.
  • Implemented a post_process_generated_files function to modify generated gRPC files for compatibility with google-cloud-spanner types and serialization methods.
• packages/google-cloud-spanner-mockserver/pyproject.toml
  • Added project metadata, dependencies (grpcio, google-cloud-spanner, protobuf, google-api-core), and optional dependencies for testing, linting, and development.
• packages/google-cloud-spanner-mockserver/spannermockserver/init.py
  • Initialized the package, defined the version, and exported key components of the mock server and test utilities.
• packages/google-cloud-spanner-mockserver/spannermockserver/generated/README.md
  • Added documentation explaining the purpose of the generated gRPC code, how to generate it, and the necessity of post-processing.
• packages/google-cloud-spanner-mockserver/spannermockserver/generated/init.py
  • Added an empty __init__.py file to mark the directory as a Python package.
• packages/google-cloud-spanner-mockserver/spannermockserver/generated/spanner_database_admin_pb2_grpc.py
  • Added generated gRPC client and server classes for the Spanner Database Admin API, with post-processing applied for type compatibility.
• packages/google-cloud-spanner-mockserver/spannermockserver/generated/spanner_pb2_grpc.py
  • Added generated gRPC client and server classes for the Spanner API, with post-processing applied for type compatibility.
• packages/google-cloud-spanner-mockserver/spannermockserver/mock_database_admin.py
  • Implemented DatabaseAdminServicer to mock the Spanner Database Admin API, including request tracking and a basic UpdateDatabaseDdl implementation.
• packages/google-cloud-spanner-mockserver/spannermockserver/mock_spanner.py
  • Implemented MockSpanner for managing mock results and errors.
  • Implemented SpannerServicer to mock the core Spanner API, handling sessions, transactions, SQL execution, and streaming results.
• packages/google-cloud-spanner-mockserver/spannermockserver/testbase/init.py
  • Initialized the testbase package and exported common test utilities.
• packages/google-cloud-spanner-mockserver/spannermockserver/testbase/mock_server_test_base.py
  • Created MockServerTestBase as a base class for tests, providing mock server setup/teardown and convenient access to Spanner client, instance, and database objects.
  • Added helper functions like add_result, set_database_dialect, add_result_select_1, and add_single_result for easy test data setup.
• packages/google-cloud-spanner-mockserver/tests/init.py
  • Added an empty __init__.py file to mark the directory as a Python package.
• packages/google-cloud-spanner-mockserver/tests/integration/init.py
  • Added an empty __init__.py file to mark the directory as a Python package.
• packages/google-cloud-spanner-mockserver/tests/integration/test_mock_spanner.py
  • Added integration tests to verify the functionality of the mock Spanner server for various operations like execute_sql, execute_streaming_sql, commit, rollback, partition_query, and partition_read.
• packages/google-cloud-spanner-mockserver/tests/unit/init.py
  • Added an empty __init__.py file to mark the directory as a Python package.
• packages/google-cloud-spanner-mockserver/tests/unit/test_mock_spanner.py
  • Added unit tests for the MockSpanner and SpannerServicer classes, covering result management, error handling, and session/transaction creation.

Activity

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[gemini-code-assist]

Code Review

This pull request introduces a new google-cloud-spanner-mockserver package, which is a great addition for testing applications that use Spanner. The overall structure, including the use of nox for automation, packaging setup, and the test base class, is well-designed. However, the mock server implementation is currently partial, with several key gRPC methods implemented as placeholders. My review focuses on suggestions to complete these placeholder implementations to make the mock server more comprehensive and useful. I've also identified a critical issue in a generated gRPC client stub that uses incorrect serialization methods, which would cause runtime failures.