Based on the research and available information, I can provide some guidance on best practices for testing flows in Prefect: 1. Regarding

prefect_test_harness

Usage: - Using

prefect_test_harness

is indeed the correct way to test flows, but there are some important considerations. - The context manager provides a temporary testing environment, but you should structure it properly. 2. Best Practices for Flow Testing:

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

   @task
   def task_1():
       return "result_1"

   @task
   def task_2():
       return "result_2"

   @flow
   def my_flow():
       t1 = task_1.submit()
       t2 = task_2.submit()
       return wait([t1, t2])

   def test_my_flow():
       with prefect_test_harness():
           result = my_flow()  # Call the flow directly, not with .fn()
           assert result == ["result_1", "result_2"]

3. Regarding Your Specific Issues: - The flakiness you're experiencing with

wait([task_1.submit(), task_2.submit()])

might be related to race conditions in your queue checking mechanism. - Instead of checking a queue for completion, consider: - Using the task results directly (they will be resolved when

wait()

completes) - Using Prefect's built-in state tracking mechanisms - If you need to test queue behavior specifically, implement proper synchronization mechanisms 4. Important Notes: - Don't use

.fn()

when testing the full flow - this bypasses Prefect's runtime context - Only use

.fn()

when you want to test the raw function logic without Prefect's orchestration - If you need logging in your tests, be aware that

get_run_logger()

requires an active flow or task context 5. For Queue Testing: If you're testing queue behavior, consider implementing a timeout mechanism:

python
   from prefect import flow, task
   import asyncio

   def test_flow_with_timeout():
       with prefect_test_harness():
           result = my_flow()
           # Add appropriate assertions for your queue state
           # Consider using asyncio.wait_for if dealing with async operations

Would you like me to provide more specific guidance about your queue checking mechanism? It would help if you could share more details about how you're implementing the queue checks in your tests.