Alternative class in Weld

In a Camel project with Weld I faced an issue while trying to unit test a route that called a remote system (Elasticsearch). This was done with the help of a custom bean. The bean handles the connection and the actual calls to the system. I did not want to call the actual system during my Unit Test, so I created a stub. However, to create the context and start the route I used CamelCdiRunner. This meant that the original client bean was being loaded. So I had to replace the actual bean with my stub. Luckily Weld supports the use of alternative beans. In essence you can replace a bean with an alternative, in my case a stub.

The first thing you need to do is to make sure that your class is based on a interface. This enables Weld to successfully replace your bean with a alternative. Inject the bean based on the interface and not on the class itself.

@Inject
@Named("elasticsearchCamelClient")
ElasticsearchCamelClientInterface client;

Next create your mock and make sure that it implements the interface of the bean you want to replace. Add the Alternative annotation.

@Alternative
@Named("elasticsearchCamelClient")
public class MockElasticsearchCamelClient implements ElasticsearchCamelClientInterface {

  public MockElasticsearchCamelClient() {
  }

  Stub code.....

Most of the documentation I found shows you how to use an alternative bean using the beans.xml file. However it is not possible to simply add a beans.xml file to the test resources. You can only specify one for your project. You could replace it dynamically with your build tool. This however is, imho, not a nice solution. Luckily you can also specify an alternative class in your test class. By adding the “@Beans” annotation. This allows you to specify one or more alternative beans.

@RunWith(CamelCdiRunner.class)
@Beans(
  alternatives = {MockElasticsearchCamelClient.class}
)
public class RouteTest { ...

The alternatives indicates that you want to run the CamelCdiRunner with the stub. When you now start the Unit Test you will see that both beans are being loaded but that the mock is used to run your tests.

Happy testing!

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