When working with external services in a Grails project, say a service that uploads files to Amazon S3 or verifies bank account information, you’ll likely want to avoid accessing these services in standard integration and functional tests. Hitting these services exposes your tests to failures caused by the service being slow or being down all together, or a whole host of other failures that are unrelated to you code. Not to mention some services, like the aforementioned bank account verification service, may have a per-use fee. You don’t want to get charged each time you run your normal test suite.

If the code that accesses the third-party service is isolated into a Grails service, it’s fairly easily to override those services in an integration test. But how to avoid hitting the ‘real’ third-party web service in a functional test?

One way to keep your tests isolated to your code and avoid a dependence on a third-party service is to create a mock implementation of your the Grails service and use Grails dependency injection to override that service bean in the test environment.

And in the resources.groovy bean definitions, explicitly override that service in the test environment.

Now, since this mock service has to live in the actual codebase for the bean override to work (under grails-app/services in this example), the mock service will by included in the war file by default. You don’t want this mock service in the production war, so one way to exclude is to explicitly delete it’s package from the war:

Then you can include all your mock services in one package, and each subsequent mock service will be removed from the production war.

And the functional test that uses the mock S3 file upload service could look something like this:

This is an example of the convenience of combining bean overriding with Grails environment-specific code to mock out third-party services.