test: Add DBAPI 2.0 compliance test suite

[bhatt4982]

test: Add DBAPI 2.0 compliance test suite including a base test class, SQL factory, helper utilities, and nox integration.

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Fixes #16120 🦕

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the testing infrastructure by introducing a robust DBAPI 2.0 compliance test suite. The new tests are designed to verify that the google-cloud-spanner-dbapi-driver adheres to the Python Database API Specification v2.0, ensuring standardized and predictable behavior. This addition improves the reliability and maintainability of the driver by systematically validating its core functionalities against industry standards.

Highlights

• New Compliance Test Suite: A new DBAPI 2.0 compliance test suite has been added, including a base test class, SQL factory, and helper utilities.
• Nox Integration: A dedicated compliance Nox session was introduced to easily run the new DBAPI 2.0 compliance tests.
• SQL Factory for Dialects: An abstract SQL factory was implemented to generate SQL statements, with a concrete implementation for GoogleSQL, facilitating dialect-specific testing.
• Comprehensive DBAPI 2.0 Checks: The base test class includes extensive checks for module attributes, connection object methods, cursor object functionalities, and type object constructors as per PEP 249.

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[gemini-code-assist]

Code Review

This pull request introduces a DBAPI 2.0 compliance test suite, which is a great addition for ensuring driver compatibility. The changes include a new nox session for running these tests, a base test class, a SQL factory for generating test data, and helper utilities. My review focuses on improving the robustness and correctness of the new test infrastructure. I've identified a critical issue in the nox configuration that would prevent the tests from running correctly, and a couple of medium-severity issues related to code robustness and error handling in the test helpers and base class.

[gemini-code-assist]

The test process requires the SPANNER_EMULATOR_HOST and TEST_DIALECT environment variables, but they are not being passed to session.run. An empty env dictionary is provided, which means the test environment will not have these crucial variables set, causing the tests to fail. You should pass these variables from the nox environment to the test execution environment.

        env={
            "SPANNER_EMULATOR_HOST": os.environ["SPANNER_EMULATOR_HOST"],
            "TEST_DIALECT": os.environ.get("TEST_DIALECT", "GoogleSQL"),
        },

[gemini-code-assist]

Using os.environ['SPANNER_EMULATOR_HOST'] can raise a KeyError if the environment variable is not set. Although the nox session checks for this, running tests manually without nox could lead to a crash. It's safer to use the module-level SPANNER_EMULATOR_HOST variable, which is already populated using os.environ.get() and is available in the scope of this function.

Suggested change

	print(f"Set SPANNER_EMULATOR_HOST to {os.environ['SPANNER_EMULATOR_HOST']}")
	print(f"Set SPANNER_EMULATOR_HOST to {SPANNER_EMULATOR_HOST}")

[gemini-code-assist]

The broad except Exception: pass in the cleanup method silently swallows all exceptions, which can hide important issues during test teardown. This makes debugging failures much harder. It's better to catch more specific exceptions or at least log the error that occurred.