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<@U0667DNC02Y> How can I test an asset that is tri...
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t
@Scout How can I test an asset that is triggered by a job? The asset contains an API call. I would like to assert that the API call happened.
s
When writing unit tests for assets in Dagster, you can treat the function decorated by 
@asset
as a regular Python function. This means you can directly invoke the decorated function in your test code and assert the expected behavior. For an asset that contains an API call, you would typically want to mock the API call to avoid making actual HTTP requests during testing. This can be done using a mocking library like 
unittest.mock
in Python. Here's a general approach to testing an asset with an API call: 1. Mock the API call. 2. Invoke the asset function directly in your test. 3. Assert that the API call was made with the expected parameters. 4. Optionally, assert the return value of the asset function if it depends on the API call's response. Here's an example of how you might write a test for such an asset:
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python from unittest.mock import patch from my_assets_module import my_asset_with_api_call  # Mock the API call @patch('my_assets_module.requests.get') def test_my_asset_with_api_call(mock_get):     # Configure the mock to return a specific response     mock_get.return_value.json.return_value = {"expected": "response"}      # Invoke the asset function     result = my_asset_with_api_call()      # Assert that the API call was made as expected     mock_get.assert_called_once_with('<http://example.com/api>')      # Assert the result of the asset function     assert result == {"expected": "response"}
In this example, 
my_assets_module.requests.get
is the path to the 
requests.get
function that is called within your asset. The 
patch
decorator from 
unittest.mock
is used to replace the 
requests.get
call with a mock that you can configure and inspect. Please note that the actual implementation of your test will depend on the specifics of your asset function and the API it calls. The above example is a simplified illustration of the approach. If your asset is part of a job and you want to test the job execution, you can use 
execute_in_process
on the job definition to execute the job in the test environment. However, you would still use mocking to intercept the API call within the asset. Remember to follow best practices for unit testing, such as isolating the unit under test and avoiding side effects like real network calls.
To test an asset that contains an API call and is triggered by a job, you can follow the general approach for testing assets as described in the documentation. Here's a step-by-step guide based on the documentation: 1. Isolate the Asset for Testing: Treat the function decorated by 
@asset
as a regular Python function. This allows you to test the asset in isolation from the job that triggers it. 2. Mock the API Call: Since your asset contains an API call, you'll want to mock this call to avoid making actual HTTP requests during testing. You can use libraries like 
unittest.mock
in Python to replace the real API call with a mock that records whether it was called and with what arguments. 3. Invoke the Asset Function Directly: In your test, directly invoke the asset function, passing in the mock for the API call. This will execute the asset's logic without the need for the job to trigger it. 4. Assert the API Call: After invoking the asset function, use assertions to check that the API call mock was called as expected. Here's a simplified example based on the documentation:
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python from unittest.mock import Mock from dagster import asset  @asset def my_asset_with_api_call(api_client):     # Your asset logic that makes an API call     response = api_client.make_call()     return response  def test_my_asset_with_api_call():     # Create a mock for the API client     mock_api_client = Mock()     mock_api_client.make_call.return_value = "expected response"      # Invoke the asset function with the mock API client     result = my_asset_with_api_call(api_client=mock_api_client)      # Assert that the API call was made     mock_api_client.make_call.assert_called_once()      # Optionally, assert the result of the asset function     assert result == "expected response"
In this example, 
api_client
is a placeholder for whatever mechanism you use to make the API call within your asset. The mock replaces this with a controlled object that records how it's used. Remember, this approach tests the asset in isolation. If you want to test the job's behavior, including how it triggers the asset and handles the result, you would need to use a different testing strategy that involves the job execution context. However, the documentation does not provide a detailed guide on testing jobs that trigger assets with API calls, so you would need to rely on general best practices for testing Dagster jobs in that case.
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