How would you isolate SQLAlchemy database tests without hiding transaction behavior?

Separates fast rollback isolation from tests that must observe commits, multiple connections, or database concurrency.

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For ordinary repository tests, I can open a connection, begin an outer transaction, bind a Session to it, and roll the transaction back after the test. That gives each test clean data without rebuilding the database. The fixture owns the connection and Session and never exposes them across concurrent tests. I still run against the production database engine when SQL and transaction semantics matter.

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Separates fast rollback isolation from tests that must observe commits, multiple connections, or database concurrency.

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Separates fast rollback isolation from tests that must observe commits, multiple connections, or database concurrency.
For ordinary repository tests, I can open a connection, begin an outer transaction, bind a Session to it, and roll the transaction back after the test. That gives each test clean data without rebuilding the database. The fixture owns the connection and Session and never exposes them across concurrent tests. I still run against the production database engine when SQL and transaction semantics matter.
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Rollback isolation can hide behavior that requires a real commit, a second connection, or connection-pool checkout. Those tests need a separate schema, database, or uniquely owned data followed by explicit cleanup. Application code may use nested transactions or call commit, so the harness must define whether it restarts a savepoint or allows the commit to escape. I make that contract visible instead of relying on a clever fixture nobody understands.

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Sharing one Session across tests
Using rollback isolation to test real commit visibility
Running destructive cleanup against an unguarded database

How would you isolate SQLAlchemy database tests without hiding transaction behavior?

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