@Marvin what is the best way to mock a prefect block value in prefect 2.x

To mock a Prefect block value in Prefect 2.x, you can utilize the

prefect_test_harness

context manager or fixture from the

prefect.testing.utilities

module. This allows you to run flows and tasks against a temporary local SQLite database, making it suitable for testing purposes. Here's a concise example:

python
from prefect import flow
from prefect.blocks.core import Block
from prefect.testing.utilities import prefect_test_harness

# Define a custom block
class MyBlock(Block):
    value: int

# Example flow using the block
@flow
def my_flow():
    block = MyBlock.load("my-block")
    return block.value

# Test function using prefect_test_harness
def test_my_flow():
    with prefect_test_harness():
        # Save a mock block value
        mock_block = MyBlock(value=42)
        mock_block.save("my-block")
        
        # Run the flow and assert the result
        assert my_flow() == 42

This example demonstrates how to define a block, save a mock value, and test a flow using the mock. For more details, refer to the Prefect testing guide.

@Marvin can I somehow turn that into a re-usable pytest fixture?

Yes, you can create a reusable pytest fixture to mock Prefect block values. Here's how you can do it:

python
import pytest
from prefect.blocks.core import Block
from prefect.testing.utilities import prefect_test_harness

# Define a custom block
class MyBlock(Block):
    value: int

@pytest.fixture(scope="function")
def mock_my_block():
    with prefect_test_harness():
        # Save a mock block value
        mock_block = MyBlock(value=42)
        mock_block.save("my-block")
        yield

# Example flow using the block
from prefect import flow

@flow
def my_flow():
    block = MyBlock.load("my-block")
    return block.value

# Test function using the fixture
def test_my_flow(mock_my_block):
    assert my_flow() == 42

### Explanation: - Fixture Definition: The

mock_my_block

fixture uses

prefect_test_harness

to set up a temporary testing environment and saves a mock block. - Scope: The fixture is scoped to "function", meaning it's applied to each test function that uses it. - Usage: In the test function, simply include

mock_my_block

as an argument to automatically use the fixture. This setup allows you to reuse the fixture across multiple tests, ensuring consistent mock block values.