# ask-ai

Greg H

02/28/2024, 7:17 PM
How should I test a resource?


02/28/2024, 7:17 PM
To test a resource in Dagster, you can follow several best practices and patterns as outlined in the documentation. Here's a step-by-step guide based on the documentation: 1. Determine the Need for Stub Resources: Before writing tests, decide if you need to stub the resource. Stubbing is useful when the resource is relatively simple and when you want to unit test the assets and ops that use the resource without relying on the actual external service. 2. Create a Mock or Stub Resource: If you decide to stub a resource, you can create a mock or stub version of the resource that mimics the behavior of the real resource. This is particularly useful when you want to avoid making actual calls to external services during testing. 3. Use the Resource in Unit Tests: When writing unit tests for assets or ops that depend on resources, you can pass the mock or stub resource as an argument when invoking the asset or op directly. This allows you to control the behavior of the resource within the test environment. 4. Testing with Complex Resources: If the resource is complex, such as one that builds separate clients, you can use tools like the
library to fake the resource and associated client. This allows you to test the interaction with the resource without relying on the actual implementation. 5. Refactor Code to Use Resources: If multiple assets or ops interact with a service in a consistent way, or if different implementations of a service are needed in certain scenarios (like staging environments or unit tests), it's recommended to refactor the code to use resources. Here's an example of how you might test an asset that requires a resource, as shown in the documentation:
Copy code
python from dagster import asset, ConfigurableResource  class BarResource(ConfigurableResource):     my_string: str  @asset def asset_requires_bar(bar: BarResource) -> str:     return bar.my_string  def test_asset_requires_bar():     result = asset_requires_bar(bar=BarResource(my_string="bar"))     # ... additional assertions ...
In this example,
is a simple resource that is being mocked for the purpose of testing the
asset. The test directly passes a configured instance of
to the asset function. Remember to follow the documentation closely for the specific patterns and best practices that apply to your use case. If you encounter any issues or have specific requirements that are not covered by the documentation, you may need to explore additional testing strategies or seek further guidance from the Dagster community or support channels.