9. Testing
Prev Part I. Spring Cloud Stream Core Next

9. Testing

Spring Cloud Stream provides support for testing your microservice applications without connecting to a messaging system. You can do that by using the TestSupportBinder provided by the spring-cloud-stream-test-support library, which can be added as a test dependency to the application:

   <dependency>
       <groupId>org.springframework.cloud</groupId>
       <artifactId>spring-cloud-stream-test-support</artifactId>
       <scope>test</scope>
   </dependency>
[Note]Note

The TestSupportBinder uses the Spring Boot autoconfiguration mechanism to supersede the other binders found on the classpath. Therefore, when adding a binder as a dependency, make sure that the test scope is being used.

The TestSupportBinder allows users to interact with the bound channels and inspect what messages are sent and received by the application

For outbound message channels, the TestSupportBinder registers a single subscriber and retains the messages emitted by the application in a MessageCollector. They can be retrieved during tests and have assertions made against them.

The user can also send messages to inbound message channels, so that the consumer application can consume the messages. The following example shows how to test both input and output channels on a processor.

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment= SpringBootTest.WebEnvironment.RANDOM_PORT)
public class ExampleTest {

  @Autowired
  private Processor processor;

  @Autowired
  private MessageCollector messageCollector;

  @Test
  @SuppressWarnings("unchecked")
  public void testWiring() {
    Message<String> message = new GenericMessage<>("hello");
    processor.input().send(message);
    Message<String> received = (Message<String>) messageCollector.forChannel(processor.output()).poll();
    assertThat(received.getPayload(), equalTo("hello world"));
  }


  @SpringBootApplication
  @EnableBinding(Processor.class)
  public static class MyProcessor {

    @Autowired
    private Processor channels;

    @Transformer(inputChannel = Processor.INPUT, outputChannel = Processor.OUTPUT)
    public String transform(String in) {
      return in + " world";
    }
  }
}

In the example above, we are creating an application that has an input and an output channel, bound through the Processor interface. The bound interface is injected into the test so we can have access to both channels. We are sending a message on the input channel and we are using the MessageCollector provided by Spring Cloud Stream’s test support to capture the message has been sent to the output channel as a result. Once we have received the message, we can validate that the component functions correctly.

9.1 Disabling the test binder autoconfiguration

The intent behind the test binder superseding all the other binders on the classpath is to make it easy to test your applications without making changes to your production dependencies. In some cases (e.g. integration tests) it is useful to use the actual production binders instead, and that requires disabling the test binder autoconfiguration. In order to do so, you can exclude the org.springframework.cloud.stream.test.binder.TestSupportBinderAutoConfiguration class using one of the Spring Boot autoconfiguration exclusion mechanisms, as in the following example.

    @SpringBootApplication(exclude = TestSupportBinderAutoConfiguration.class)
    @EnableBinding(Processor.class)
    public static class MyProcessor {

        @Transformer(inputChannel = Processor.INPUT, outputChannel = Processor.OUTPUT)
        public String transform(String in) {
            return in + " world";
        }
    }

When autoconfiguration is disabled, the test binder is available on the classpath, and its defaultCandidate property is set to false, so that it does not interfere with the regular user configuration. It can be referenced under the name test e.g.:

spring.cloud.stream.defaultBinder=test
Prev Up Next
8. Inter-Application Communication Home 10. Health Indicator