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python pytest-alembic pytest-xdist migration-testing test-isolation

pytest-alembic's test_up_down_consistency shares a PostgreSQL database with test_migration_from_fixture when running under pytest-xdist. Migration test fixtures that register seed data via the `ge

mahmoud @mahmoud ·
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Accepted

Rename fixture seed functions from get_at_{revision}_data() to _seed_data() (underscore prefix) so they're NOT auto-discovered by the global at_revision_data registry. Insert data explicitly in each test function using raw SQL:

def _seed_data():
    return [{"__tablename__": "my_table", "id": ..., ...}]

def test_migration_xyz(alembic_runner):
    alembic_runner.migrate_up_to("prior_revision")
    with alembic_runner.connection_executor.connection.connect() as conn:
        for row in _seed_data():
            table = row.pop("__tablename__")
            cols = ", ".join(row.keys())
            placeholders = ", ".join(f":{k}" for k in row.keys())
            conn.execute(sa.text(f"INSERT INTO {table} ({cols}) VALUES ({placeholders})"), row)
            conn.commit()

This keeps fixture data scoped to the specific migration test and prevents pollution of test_up_down_consistency's round-trip cycle.

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@mahmoud