@Marvin can I mock a

@task

in a python unit test?

You can mock a Prefect

@task

in a unit test by directly accessing the underlying function using the

.fn

attribute of the

@task

decorator. Here's a simple example:

python
from prefect import flow, task

@task
def my_favorite_task():
    return 42

@flow
def my_favorite_flow():
    val = my_favorite_task()
    return val

def test_my_favorite_task():
    assert my_favorite_task.fn() == 42

In this example,

my_favorite_task.fn()

allows you to call the original function without executing the task in the Prefect runtime context. For tasks that use a logger, you can disable the logger to avoid runtime errors related to the missing flow context:

python
from prefect.logging import disable_run_logger

def test_my_favorite_task():
    with disable_run_logger():
        assert my_favorite_task.fn() == 42

For more detailed information, refer to the Testing guide from Prefect documentation. Additionally, be aware that using

prefect.get_run_logger()

directly within task code can lead to

MissingContextError

. For such use cases, consider avoiding direct logger use in unit tests or applying appropriate mocks. For details, you can check the related GitHub issue. If you have further questions, feel free to ask.

Can I mock a task call while testing the flow?

Yes, you can mock a task call while testing a flow. This allows you to test your flow logic without actually running the task. Here's a simple way to do that using the Python

unittest.mock

library: ### Example

python
from unittest.mock import patch, MagicMock
from prefect import flow, task

# Define a task
@task
def my_favorite_task():
    return 42

# Define a flow
@flow
def my_favorite_flow():
    val = my_favorite_task()
    return val

# Testing the flow and mocking the task
def test_my_favorite_flow():
    with patch("path.to.your.module.my_favorite_task", MagicMock(return_value=42)) as mock_task:
        result = my_favorite_flow()
        assert result == 42
        mock_task.assert_called_once()

# Run the test function
test_my_favorite_flow()

### Steps 1. Import the Required Modules: -

patch

and

MagicMock

from

unittest.mock

. 2. Define the Flow and Task: - Ensure your flow and task are defined in a module that you can import in your test. 3. Mock the Task Call: - Use

patch

to replace the task call with a mock that returns a predefined value. - Ensure you specify the correct import path to the task within your module. 4. Assert the Flow Execution: - Call the flow function and assert that the result is as expected. - Use

mock_task.assert_called_once()

to verify that the mocked task was called exactly once. ### Links - Refer to the Testing guide for more details. - For issues related to mocking, see the GitHub issue. This approach ensures that your unit tests focus on the flow logic and do not depend on the execution of individual tasks.