Short answer: this usually happens when the test harness spins up the local API but your environment is missing the server bits or there’s a version mismatch. Make sure you have compatible versions and the server extra installed, then register/create the block inside the harness before loading it. A quick checklist: - Confirm versions - Prefect: 3.x (latest recommended) - prefect-sqlalchemy: a 3.x–compatible release - If you recently upgraded, ensure there’s no leftover Prefect 2.x in the environment. - Install server dependencies used by `prefect_test_harness`: -

pip install "prefect[server]"

- Register the SqlAlchemyConnector block type and create a test block inside the harness - The harness starts a fresh, empty API/database; block types and instances won’t exist there unless you register/create them within the

with prefect_test_harness():

block Example pytest pattern:

import pytest
from prefect.testing.utilities import prefect_test_harness
from prefect_sqlalchemy import SqlAlchemyConnector, register_blocks

# Suppose your code under test does: SqlAlchemyConnector.load("<name>")

def test_my_fn():
    with prefect_test_harness():
        # Make the block type available in this fresh test DB
        register_blocks()  # or at least import SqlAlchemyConnector so it registers

        # Create a temporary connector block for the test
        connector = SqlAlchemyConnector(connection_url="sqlite+aiosqlite://")
        connector.save("test-conn", overwrite=True)

        # Call the function that loads/uses the block
        result = my_function_that_loads_block("test-conn")

        # Your assertion(s) here
        assert isinstance(result, list)

If you still see “NameError: name PrefectDBInterface is not defined,” it’s typically one of: - Missing server extras for local API: fix with

pip install "prefect[server]"

. - Mixed/old install (bits of Prefect 2.x lingering): recreate the venv and install Prefect 3.x cleanly, plus

prefect[server]

. - Running the harness but trying to load a block that only exists in your real workspace (not the test DB): create it inside the harness as shown above. If you share: - Your Prefect and prefect-sqlalchemy versions - How you invoke

prefect_test_harness

in the test - The exact stack trace segment where the NameError appears …I can pinpoint which of the above is the culprit and tailor the fix.

@Marvin prefect version 3.6.2 and prefect-sqlalchemy version 0.5.3

Got it — thanks! I’ve noted you’re on Prefect 3.6.2 with prefect-sqlalchemy 0.5.3. How can I help today? Are you setting up a SqlAlchemyConnector block or running into an error? If you need a quick working example, here’s a minimal pattern that works with your versions:

from prefect import flow, get_run_logger
from prefect_sqlalchemy import SqlAlchemyConnector
from sqlalchemy import text

@flow
def main():
    logger = get_run_logger()

    # Tip: source this URL from an env var or secret to avoid committing creds
    connector = SqlAlchemyConnector(
        connection_info="<postgresql+psycopg://user:pass@host:5432/dbname>"
    )

    with connector.get_connection() as conn:
        rows = conn.execute(text("SELECT 1")).all()
        <http://logger.info|logger.info>(f"Result: {rows}")

if __name__ == "__main__":
    main()

Optionally, save/load as a Block:

# one-time setup
SqlAlchemyConnector(connection_info="postgresql+psycopg://...").save("prod-db", overwrite=True)

# later in flows
connector = SqlAlchemyConnector.load("prod-db")
with connector.get_connection() as conn:
    ...

Docs: - SqlAlchemy collection: prefect-sqlalchemy docs - Blocks in Prefect 3: Blocks concept If you can share your database type and what you’re trying to run (or any error message), I can tailor the exact setup.