@Marvin Is it possible to spawn a runner process using an ephemeral API for unit testing?

Yes, it is possible to spawn a runner process using an ephemeral API for unit testing in Prefect 3.x. The ephemeral mode can be enabled by configuring the server settings. Here are some relevant settings: - Ephemeral Mode Timeout: You can set the startup timeout for the server in ephemeral mode using the environment variable

PREFECT_SERVER_EPHEMERAL_STARTUP_TIMEOUT_SECONDS

. - Event Streaming: The server can stream events to the API via WebSockets, controlled by

PREFECT_SERVER_EVENTS_STREAM_OUT_ENABLED

. For unit testing, Prefect relies on writing tests using frameworks like

pytest

, and it is recommended to write tests that fail before your changes and pass afterward to ensure robustness. For more details, you can refer to the Prefect documentation on ephemeral mode settings. If you need to explore more about Prefect's public API or specific modules, you can start with the top-level API which includes functions like

flow

,

task

,

get_client

, and more. You can explore further based on your specific needs. Let me know if there's anything else you need!

@Marvin Can you give me the example code for spawning a runner using an ephemeral API server? A pytest fixture would be preferable.

Here's an example of how you can create a pytest fixture to spawn a runner using an ephemeral API server in Prefect 3.x. This example uses the

prefect_test_harness

utility to set up a temporary Prefect database/server for testing:

python
import pytest
from prefect.testing.utilities import prefect_test_harness
from prefect import flow, task

@pytest.fixture(autouse=True)
def prefect_db():
    with prefect_test_harness() as harness:
        """Sets up a temp sandbox Prefect database/server for running tests."""
        yield harness

@task
def say_hello(name: str) -> str:
    return f"Hello, {name}!"

@flow
def greet(name: str):
    return say_hello(name)

def test_greet(prefect_db):
    result = greet("World")
    assert result == "Hello, World!"

In this example: -

prefect_test_harness()

sets up a temporary Prefect environment for testing. - A simple

flow

and

task

are defined to demonstrate the functionality. - The

test_greet

function uses the fixture to ensure the Prefect environment is available during the test. For more details on Prefect testing utilities, you can refer to the Prefect testing documentation.