Problem

Spanner system tests can sometimes leave behind test databases if a run is interrupted or fails to clean up properly. Over time, these stale databases can accumulate, potentially hitting quota limits or cluttering the test environment.

Solution

Introduced a proactive cleanup mechanism to remove stale databases during test setup.

• Added cleanup_stale_databases helper: A new function in _helpers.py that lists databases in a given instance and drops any that are older than a specified cutoff (defaulting to 10 minutes/600 seconds).
• Drop Protection Handling: The helper explicitly disables enable_drop_protection if it's set, ensuring that even protected test databases can be cleaned up automatically.
• Fixture Integration: Integrated this cleanup call into the shared_instance fixture in conftest.py, ensuring that every test session starts by cleaning up residue from previous runs.

Impact

• Reduces the risk of test failures due to database quota exhaustion.
• Keeps the Spanner instance used for testing clean.
• Resilient against partial failures by handling NotFound and other API errors during cleanup.