5. Spring Cloud Contract Verifier Messaging
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5. Spring Cloud Contract Verifier Messaging

Spring Cloud Contract Verifier lets you verify applications that use messaging as a means of communication. All of the integrations shown in this document work with Spring, but you can also create one of your own and use that.

5.1 Integrations

You can use one of the following four integration configurations:

Apache Camel
Spring Integration
Spring Cloud Stream
Spring AMQP

Since we use Spring Boot, if you have added one of these libraries to the classpath, all the messaging configuration is automatically set up.

	Important
	Remember to put `@AutoConfigureMessageVerifier` on the base class of your generated tests. Otherwise, messaging part of Spring Cloud Contract Verifier does not work.

	Important
	If you want to use Spring Cloud Stream, remember to add a dependency on `org.springframework.cloud:spring-cloud-stream-test-support`, as shown here:

Maven.

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

Gradle.

testCompile "org.springframework.cloud:spring-cloud-stream-test-support"

5.2 Manual Integration Testing

The main interface used by the tests is org.springframework.cloud.contract.verifier.messaging.MessageVerifier. It defines how to send and receive messages. You can create your own implementation to achieve the same goal.

In a test, you can inject a ContractVerifierMessageExchange to send and receive messages that follow the contract. Then add @AutoConfigureMessageVerifier to your test. Here’s an example:

@RunWith(SpringTestRunner.class)
@SpringBootTest
@AutoConfigureMessageVerifier
public static class MessagingContractTests {

  @Autowired
  private MessageVerifier verifier;
  ...
}

	Note
	If your tests require stubs as well, then `@AutoConfigureStubRunner` includes the messaging configuration, so you only need the one annotation.

5.3 Publisher-Side Test Generation

Having the input or outputMessage sections in your DSL results in creation of tests on the publisher’s side. By default, JUnit tests are created. However, there is also a possibility to create Spock tests.

There are 3 main scenarios that we should take into consideration:

Scenario 1: There is no input message that produces an output message. The output message is triggered by a component inside the application (for example, scheduler).
Scenario 2: The input message triggers an output message.
Scenario 3: The input message is consumed and there is no output message.

	Important
	The destination passed to `messageFrom` or `sentTo` can have different meanings for different messaging implementations. For Stream and Integration it is first resolved as a `destination` of a channel. Then, if there is no such `destination` it is resolved as a channel name. For Camel, that’s a certain component (for example, `jms`).

5.3.1 Scenario 1: No Input Message

For the given contract:

Groovy DSL.

def contractDsl = Contract.make {
	label 'some_label'
	input {
		triggeredBy('bookReturnedTriggered()')
	}
	outputMessage {
		sentTo('activemq:output')
		body('''{ "bookName" : "foo" }''')
		headers {
			header('BOOK-NAME', 'foo')
			messagingContentType(applicationJson())
		}
	}
}

YAML.

label: some_label
input:
  triggeredBy: bookReturnedTriggered
outputMessage:
  sentTo: activemq:output
  body:
    bookName: foo
  headers:
    BOOK-NAME: foo
    contentType: application/json

The following JUnit test is created:

'''
 // when:
  bookReturnedTriggered();

 // then:
  ContractVerifierMessage response = contractVerifierMessaging.receive("activemq:output");
  assertThat(response).isNotNull();
  assertThat(response.getHeader("BOOK-NAME")).isNotNull();
  assertThat(response.getHeader("BOOK-NAME").toString()).isEqualTo("foo");
  assertThat(response.getHeader("contentType")).isNotNull();
  assertThat(response.getHeader("contentType").toString()).isEqualTo("application/json");
 // and:
  DocumentContext parsedJson = JsonPath.parse(contractVerifierObjectMapper.writeValueAsString(response.getPayload()));
  assertThatJson(parsedJson).field("bookName").isEqualTo("foo");
'''

And the following Spock test would be created:

'''
 when:
  bookReturnedTriggered()

 then:
  ContractVerifierMessage response = contractVerifierMessaging.receive('activemq:output')
  assert response != null
  response.getHeader('BOOK-NAME')?.toString()  == 'foo'
  response.getHeader('contentType')?.toString()  == 'application/json'
 and:
  DocumentContext parsedJson = JsonPath.parse(contractVerifierObjectMapper.writeValueAsString(response.payload))
  assertThatJson(parsedJson).field("bookName").isEqualTo("foo")

'''

5.3.2 Scenario 2: Output Triggered by Input

For the given contract:

Groovy DSL.

def contractDsl = Contract.make {
	label 'some_label'
	input {
		messageFrom('jms:input')
		messageBody([
				bookName: 'foo'
		])
		messageHeaders {
			header('sample', 'header')
		}
	}
	outputMessage {
		sentTo('jms:output')
		body([
				bookName: 'foo'
		])
		headers {
			header('BOOK-NAME', 'foo')
		}
	}
}

YAML.

label: some_label
input:
  messageFrom: jms:input
  messageBody:
    bookName: 'foo'
  messageHeaders:
    sample: header
outputMessage:
  sentTo: jms:output
  body:
    bookName: foo
  headers:
    BOOK-NAME: foo

The following JUnit test is created:

'''
// given:
 ContractVerifierMessage inputMessage = contractVerifierMessaging.create(
  "{\\"bookName\\":\\"foo\\"}"
, headers()
  .header("sample", "header"));

// when:
 contractVerifierMessaging.send(inputMessage, "jms:input");

// then:
 ContractVerifierMessage response = contractVerifierMessaging.receive("jms:output");
 assertThat(response).isNotNull();
 assertThat(response.getHeader("BOOK-NAME")).isNotNull();
 assertThat(response.getHeader("BOOK-NAME").toString()).isEqualTo("foo");
// and:
 DocumentContext parsedJson = JsonPath.parse(contractVerifierObjectMapper.writeValueAsString(response.getPayload()));
 assertThatJson(parsedJson).field("bookName").isEqualTo("foo");
'''

And the following Spock test would be created:

"""\
given:
   ContractVerifierMessage inputMessage = contractVerifierMessaging.create(
    '''{"bookName":"foo"}''',
    ['sample': 'header']
  )

when:
   contractVerifierMessaging.send(inputMessage, 'jms:input')

then:
   ContractVerifierMessage response = contractVerifierMessaging.receive('jms:output')
   assert response !- null
   response.getHeader('BOOK-NAME')?.toString()  == 'foo'
and:
   DocumentContext parsedJson = JsonPath.parse(contractVerifierObjectMapper.writeValueAsString(response.payload))
   assertThatJson(parsedJson).field("bookName").isEqualTo("foo")
"""

5.3.3 Scenario 3: No Output Message

For the given contract:

Groovy DSL.

def contractDsl = Contract.make {
	label 'some_label'
	input {
		messageFrom('jms:delete')
		messageBody([
				bookName: 'foo'
		])
		messageHeaders {
			header('sample', 'header')
		}
		assertThat('bookWasDeleted()')
	}
}

YAML.

label: some_label
input:
  messageFrom: jms:delete
  messageBody:
    bookName: 'foo'
  messageHeaders:
    sample: header
  assertThat: bookWasDeleted()

The following JUnit test is created:

'''
// given:
 ContractVerifierMessage inputMessage = contractVerifierMessaging.create(
	"{\\"bookName\\":\\"foo\\"}"
, headers()
	.header("sample", "header"));

// when:
 contractVerifierMessaging.send(inputMessage, "jms:delete");

// then:
 bookWasDeleted();
'''

And the following Spock test would be created:

'''
given:
	 ContractVerifierMessage inputMessage = contractVerifierMessaging.create(
		\'\'\'{"bookName":"foo"}\'\'\',
		['sample': 'header']
	)

when:
	 contractVerifierMessaging.send(inputMessage, 'jms:delete')

then:
	 noExceptionThrown()
	 bookWasDeleted()
'''

5.4 Consumer Stub Generation

Unlike the HTTP part, in messaging, we need to publish the Groovy DSL inside the JAR with a stub. Then it is parsed on the consumer side and proper stubbed routes are created.

For more information, see Chapter 7, Stub Runner for Messaging section.

Maven.

<dependencies>
	<dependency>
		<groupId>org.springframework.cloud</groupId>
		<artifactId>spring-cloud-starter-stream-rabbit</artifactId>
	</dependency>

	<dependency>
		<groupId>org.springframework.cloud</groupId>
		<artifactId>spring-cloud-starter-contract-stub-runner</artifactId>
		<scope>test</scope>
	</dependency>
	<dependency>
		<groupId>org.springframework.cloud</groupId>
		<artifactId>spring-cloud-stream-test-support</artifactId>
		<scope>test</scope>
	</dependency>
</dependencies>

<dependencyManagement>
	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-dependencies</artifactId>
			<version>Finchley.BUILD-SNAPSHOT</version>
			<type>pom</type>
			<scope>import</scope>
		</dependency>
	</dependencies>
</dependencyManagement>

Gradle.

ext {
	contractsDir = file("mappings")
	stubsOutputDirRoot = file("${project.buildDir}/production/${project.name}-stubs/")
}

// Automatically added by plugin:
// copyContracts - copies contracts to the output folder from which JAR will be created
// verifierStubsJar - JAR with a provided stub suffix
// the presented publication is also added by the plugin but you can modify it as you wish

publishing {
	publications {
		stubs(MavenPublication) {
			artifactId "${project.name}-stubs"
			artifact verifierStubsJar
		}
	}
}

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