Add a test slice and autoconfiguration for the new test binder

When using Spring Cloud Contract, in order to integrate with the new testing binder, we need to, in the base class, start a Spring Boot context AND manually import the testing binder configuration.

What we would like to achieve is that the testing binder configuration gets automatically discovered and applied in the context of a test. Also a test slice with @ImportAutoConfiguration that imports all of the configuration classes would come in handy.

Production code

@SpringBootApplication
public class DemoApplication {

	public static void main(String[] args) {
		SpringApplication.run(DemoApplication.class, args);
	}

	@Bean
	EmitterProcessor<Fraud> emitterProcessor() {
		return EmitterProcessor.create();
	}

	@Bean
	Supplier<Flux<Fraud>> frauds(EmitterProcessor<Fraud> emitterProcessor) {
		return () -> emitterProcessor;
	}

}

@RestController
class FraudController {
	private final EmitterProcessor<Fraud> emitter;

	FraudController(EmitterProcessor<Fraud> emitter) {
		this.emitter = emitter;
	}

	@PostMapping("/trigger")
	void trigger() {
		Fraud fraud = new Fraud("g");
		System.out.println("GOT " + fraud);
		emitter.onNext(fraud);
	}
}

class Fraud {
	String surname;

	public Fraud(String surname) {
		this.surname = surname;
	}

	public Fraud() {
	}

	public String getSurname() {
		return surname;
	}

	public void setSurname(String surname) {
		this.surname = surname;
	}
}

Base class (the one that requires configuration setup)

import org.springframework.cloud.contract.verifier.messaging.boot.AutoConfigureMessageVerifier;

@SpringBootTest(classes = BaseClass.SampleConfiguration.class)
@AutoConfigureMessageVerifier
public class BaseClass {

	@Autowired
	FraudController fraudController;

	public void trigger() {
		fraudController.trigger();
	}

	@EnableAutoConfiguration
	@Import({TestChannelBinderConfiguration.class, DemoApplication.class})
	public static class SampleConfiguration {

	}

}

Start by tracing the @AutoConfigureMessageVerifier entry point and the TestChannelBinderConfiguration used in BaseClass.SampleConfiguration. The work is done when testing binder configuration is discovered automatically and a test slice using @ImportAutoConfiguration imports the required configuration classes without the manual imports shown.