Based on the research and GitHub issues, I can help you fix this testing issue. The error you're encountering is because you're trying to access the

.fn

attribute directly on the task function, but there's a slight difference in how you need to test tasks in Prefect 3.x. Here's how to fix it: 1. First, make sure your task is properly decorated with `@task`:

python
from prefect import task

@task
def my_favorite_task():
    return 42

2. Then, in your test, you need to access the underlying function in one of two ways:

python
from prefect.logging import disable_run_logger

def test_my_favorite_task():
    # Option 1: Use .fn() directly on the task
    with disable_run_logger():
        assert my_favorite_task.fn() == 42
        
    # Option 2: Call the task directly (preferred method)
    with disable_run_logger():
        assert my_favorite_task() == 42

The error you're seeing (

AttributeError: 'function' object has no attribute 'fn'

) suggests that either: 1. The function isn't properly decorated with

@task

, or 2. You're trying to access

.fn

on the raw function instead of the task object For the most robust testing approach in Prefect 3.x, I recommend using the test harness:

python
from prefect.testing.utilities import prefect_test_harness
import pytest

@pytest.fixture(autouse=True)
def test_harness():
    with prefect_test_harness():
        yield

def test_my_favorite_task():
    result = my_favorite_task()
    assert result == 42

This approach provides a complete test environment and handles the logging context automatically. Remember that in Prefect 3.x, you can call tasks directly in tests without needing to access the

.fn

attribute in most cases. The

.fn

attribute is still available but is less commonly needed than in previous versions. Links: - Testing Workflows Documentation - Prefect Testing Utilities