2. Spring Cloud Contract Verifier Introduction

If we wanted to test the application in top left corner to determine whether it can communicate with other services, we could do one of two things:

Both have their advantages but also a lot of disadvantages.

Deploy all microservices and perform end to end tests

Advantages:

Disadvantages:

Mock other microservices in unit/integration tests

Advantages:

Disadvantages:

To solve the aforementioned issues, Spring Cloud Contract Verifier with Stub Runner was created. The main idea is to give you very fast feedback, without the need to set up the whole world of microservices. If you work on stubs, then the only applications you need are those that your application directly uses.

Spring Cloud Contract Verifier gives you the certainty that the stubs that you use were created by the service that you’re calling. Also, if you can use them, it means that they were tested against the producer’s side. In short, you can trust those stubs.

As consumers of services, we need to define what exactly we want to achieve. We need to formulate our expectations. That is why we write contracts.

Assume that you want to send a request containing the ID of a client company and the amount it wants to borrow from us. You also want to send it to the /fraudcheck url via the PUT method.

Groovy DSL. 

package contracts

org.springframework.cloud.contract.spec.Contract.make {
	request { // (1)
		method 'PUT' // (2)
		url '/fraudcheck' // (3)
		body([ // (4)
			   "client.id": $(regex('[0-9]{10}')),
			   loanAmount: 99999
		])
		headers { // (5)
			contentType('application/json')
		}
	}
	response { // (6)
		status 200 // (7)
		body([ // (8)
			   fraudCheckStatus: "FRAUD",
			   "rejection.reason": "Amount too high"
		])
		headers { // (9)
			contentType('application/json')
		}
	}
}

/*
From the Consumer perspective, when shooting a request in the integration test:

(1) - If the consumer sends a request
(2) - With the "PUT" method
(3) - to the URL "/fraudcheck"
(4) - with the JSON body that
 * has a field `client.id` that matches a regular expression `[0-9]{10}`
 * has a field `loanAmount` that is equal to `99999`
(5) - with header `Content-Type` equal to `application/json`
(6) - then the response will be sent with
(7) - status equal `200`
(8) - and JSON body equal to
 { "fraudCheckStatus": "FRAUD", "rejectionReason": "Amount too high" }
(9) - with header `Content-Type` equal to `application/json`

From the Producer perspective, in the autogenerated producer-side test:

(1) - A request will be sent to the producer
(2) - With the "PUT" method
(3) - to the URL "/fraudcheck"
(4) - with the JSON body that
 * has a field `client.id` that will have a generated value that matches a regular expression `[0-9]{10}`
 * has a field `loanAmount` that is equal to `99999`
(5) - with header `Content-Type` equal to `application/json`
(6) - then the test will assert if the response has been sent with
(7) - status equal `200`
(8) - and JSON body equal to
 { "fraudCheckStatus": "FRAUD", "rejectionReason": "Amount too high" }
(9) - with header `Content-Type` matching `application/json.*`
 */

YAML. 

request: # (1)
  method: PUT # (2)
  url: /fraudcheck # (3)
  body: # (4)
    "client.id": 1234567890
    loanAmount: 99999
  headers: # (5)
    Content-Type: application/json
  matchers:
    body:
      - path: $.['client.id'] # (6)
        type: by_regex
        value: "[0-9]{10}"
response: # (7)
  status: 200 # (8)
  body:  # (9)
    fraudCheckStatus: "FRAUD"
    "rejection.reason": "Amount too high"
  headers: # (10)
    Content-Type: application/json;charset=UTF-8


#From the Consumer perspective, when shooting a request in the integration test:
#
#(1) - If the consumer sends a request
#(2) - With the "PUT" method
#(3) - to the URL "/fraudcheck"
#(4) - with the JSON body that
# * has a field `client.id`
# * has a field `loanAmount` that is equal to `99999`
#(5) - with header `Content-Type` equal to `application/json`
#(6) - and a `client.id` json entry matches the regular expression `[0-9]{10}`
#(7) - then the response will be sent with
#(8) - status equal `200`
#(9) - and JSON body equal to
# { "fraudCheckStatus": "FRAUD", "rejectionReason": "Amount too high" }
#(10) - with header `Content-Type` equal to `application/json`
#
#From the Producer perspective, in the autogenerated producer-side test:
#
#(1) - A request will be sent to the producer
#(2) - With the "PUT" method
#(3) - to the URL "/fraudcheck"
#(4) - with the JSON body that
# * has a field `client.id` `1234567890`
# * has a field `loanAmount` that is equal to `99999`
#(5) - with header `Content-Type` equal to `application/json`
#(7) - then the test will assert if the response has been sent with
#(8) - status equal `200`
#(9) - and JSON body equal to
# { "fraudCheckStatus": "FRAUD", "rejectionReason": "Amount too high" }
#(10) - with header `Content-Type` equal to `application/json;charset=UTF-8`

Spring Cloud Contract generates stubs, which you can use during client-side testing. You get a running WireMock instance/Messaging route that simulates the service. You would like to feed that instance with a proper stub definition.

At some point in time, you need to send a request to the Fraud Detection service.

ResponseEntity<FraudServiceResponse> response =
		restTemplate.exchange("http://localhost:" + port + "/fraudcheck", HttpMethod.PUT,
				new HttpEntity<>(request, httpHeaders),
				FraudServiceResponse.class);

Annotate your test class with @AutoConfigureStubRunner. In the annotation provide the group id and artifact id for the Stub Runner to download stubs of your collaborators.

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment=WebEnvironment.NONE)
@AutoConfigureStubRunner(ids = {"com.example:http-server-dsl:+:stubs:6565"}, workOffline = true)
public class LoanApplicationServiceTests {

After that, during the tests, Spring Cloud Contract automatically finds the stubs (simulating the real service) in the Maven repository and exposes them on a configured (or random) port.

Since you are developing your stub, you need to be sure that it actually resembles your concrete implementation. You cannot have a situation where your stub acts in one way and your application behaves in a different way, especially in production.

To ensure that your application behaves the way you define in your stub, tests are generated from the stub you provide.

The autogenerated test looks, more or less, like this:

@Test
public void validate_shouldMarkClientAsFraud() throws Exception {
    // given:
        MockMvcRequestSpecification request = given()
                .header("Content-Type", "application/vnd.fraud.v1+json")
                .body("{\"client.id\":\"1234567890\",\"loanAmount\":99999}");

    // when:
        ResponseOptions response = given().spec(request)
                .put("/fraudcheck");

    // then:
        assertThat(response.statusCode()).isEqualTo(200);
        assertThat(response.header("Content-Type")).matches("application/vnd.fraud.v1.json.*");
    // and:
        DocumentContext parsedJson = JsonPath.parse(response.getBody().asString());
        assertThatJson(parsedJson).field("['fraudCheckStatus']").matches("[A-Z]{5}");
        assertThatJson(parsedJson).field("['rejection.reason']").isEqualTo("Amount too high");
}

If using the SNAPSHOT / Milestone / Release Candidate versions please add the following section to your build:

Maven. 

<repositories>
	<repository>
		<id>spring-snapshots</id>
		<name>Spring Snapshots</name>
		<url>https://repo.spring.io/snapshot</url>
		<snapshots>
			<enabled>true</enabled>
		</snapshots>
	</repository>
	<repository>
		<id>spring-milestones</id>
		<name>Spring Milestones</name>
		<url>https://repo.spring.io/milestone</url>
		<snapshots>
			<enabled>false</enabled>
		</snapshots>
	</repository>
	<repository>
		<id>spring-releases</id>
		<name>Spring Releases</name>
		<url>https://repo.spring.io/release</url>
		<snapshots>
			<enabled>false</enabled>
		</snapshots>
	</repository>
</repositories>
<pluginRepositories>
	<pluginRepository>
		<id>spring-snapshots</id>
		<name>Spring Snapshots</name>
		<url>https://repo.spring.io/snapshot</url>
		<snapshots>
			<enabled>true</enabled>
		</snapshots>
	</pluginRepository>
	<pluginRepository>
		<id>spring-milestones</id>
		<name>Spring Milestones</name>
		<url>https://repo.spring.io/milestone</url>
		<snapshots>
			<enabled>false</enabled>
		</snapshots>
	</pluginRepository>
	<pluginRepository>
		<id>spring-releases</id>
		<name>Spring Releases</name>
		<url>https://repo.spring.io/release</url>
		<snapshots>
			<enabled>false</enabled>
		</snapshots>
	</pluginRepository>
</pluginRepositories>

Gradle. 

repositories {
	mavenCentral()
	mavenLocal()
	maven { url "https://repo.spring.io/snapshot" }
	maven { url "https://repo.spring.io/milestone" }
	maven { url "https://repo.spring.io/release" }
}

As a developer of the Loan Issuance service (a consumer of the Fraud Detection server), you might do the following steps:

Start doing TDD by writing a test for your feature.

@Test
public void shouldBeRejectedDueToAbnormalLoanAmount() {
	// given:
	LoanApplication application = new LoanApplication(new Client("1234567890"),
			99999);
	// when:
	LoanApplicationResult loanApplication = service.loanApplication(application);
	// then:
	assertThat(loanApplication.getLoanApplicationStatus())
			.isEqualTo(LoanApplicationStatus.LOAN_APPLICATION_REJECTED);
	assertThat(loanApplication.getRejectionReason()).isEqualTo("Amount too high");
}

Assume that you have written a test of your new feature. If a loan application for a big amount is received, the system should reject that loan application with some description.

Write the missing implementation.

At some point in time, you need to send a request to the Fraud Detection service. Assume that you need to send the request containing the ID of the client and the amount the client wants to borrow. You want to send it to the /fraudcheck url via the PUT method.

ResponseEntity<FraudServiceResponse> response =
		restTemplate.exchange("http://localhost:" + port + "/fraudcheck", HttpMethod.PUT,
				new HttpEntity<>(request, httpHeaders),
				FraudServiceResponse.class);

For simplicity, the port of the Fraud Detection service is set to 8080, and the application runs on 8090.

If you start the test at this point, it breaks, because no service currently runs on port 8080.

Clone the Fraud Detection service repository locally.

You can start by playing around with the server side contract. To do so, you must first clone it.

$ git clone https://your-git-server.com/server-side.git local-http-server-repo

Define the contract locally in the repo of Fraud Detection service.

As a consumer, you need to define what exactly you want to achieve. You need to formulate your expectations. To do so, write the following contract:

	Important
	Place the contract under src/test/resources/contracts/fraud folder. The fraud folder is important because the producer’s test base class name references that folder.

Groovy DSL. 

package contracts

org.springframework.cloud.contract.spec.Contract.make {
	request { // (1)
		method 'PUT' // (2)
		url '/fraudcheck' // (3)
		body([ // (4)
			   "client.id": $(regex('[0-9]{10}')),
			   loanAmount: 99999
		])
		headers { // (5)
			contentType('application/json')
		}
	}
	response { // (6)
		status 200 // (7)
		body([ // (8)
			   fraudCheckStatus: "FRAUD",
			   "rejection.reason": "Amount too high"
		])
		headers { // (9)
			contentType('application/json')
		}
	}
}

/*
From the Consumer perspective, when shooting a request in the integration test:

(1) - If the consumer sends a request
(2) - With the "PUT" method
(3) - to the URL "/fraudcheck"
(4) - with the JSON body that
 * has a field `client.id` that matches a regular expression `[0-9]{10}`
 * has a field `loanAmount` that is equal to `99999`
(5) - with header `Content-Type` equal to `application/json`
(6) - then the response will be sent with
(7) - status equal `200`
(8) - and JSON body equal to
 { "fraudCheckStatus": "FRAUD", "rejectionReason": "Amount too high" }
(9) - with header `Content-Type` equal to `application/json`

From the Producer perspective, in the autogenerated producer-side test:

(1) - A request will be sent to the producer
(2) - With the "PUT" method
(3) - to the URL "/fraudcheck"
(4) - with the JSON body that
 * has a field `client.id` that will have a generated value that matches a regular expression `[0-9]{10}`
 * has a field `loanAmount` that is equal to `99999`
(5) - with header `Content-Type` equal to `application/json`
(6) - then the test will assert if the response has been sent with
(7) - status equal `200`
(8) - and JSON body equal to
 { "fraudCheckStatus": "FRAUD", "rejectionReason": "Amount too high" }
(9) - with header `Content-Type` matching `application/json.*`
 */

YAML. 

request: # (1)
  method: PUT # (2)
  url: /fraudcheck # (3)
  body: # (4)
    "client.id": 1234567890
    loanAmount: 99999
  headers: # (5)
    Content-Type: application/json
  matchers:
    body:
      - path: $.['client.id'] # (6)
        type: by_regex
        value: "[0-9]{10}"
response: # (7)
  status: 200 # (8)
  body:  # (9)
    fraudCheckStatus: "FRAUD"
    "rejection.reason": "Amount too high"
  headers: # (10)
    Content-Type: application/json;charset=UTF-8


#From the Consumer perspective, when shooting a request in the integration test:
#
#(1) - If the consumer sends a request
#(2) - With the "PUT" method
#(3) - to the URL "/fraudcheck"
#(4) - with the JSON body that
# * has a field `client.id`
# * has a field `loanAmount` that is equal to `99999`
#(5) - with header `Content-Type` equal to `application/json`
#(6) - and a `client.id` json entry matches the regular expression `[0-9]{10}`
#(7) - then the response will be sent with
#(8) - status equal `200`
#(9) - and JSON body equal to
# { "fraudCheckStatus": "FRAUD", "rejectionReason": "Amount too high" }
#(10) - with header `Content-Type` equal to `application/json`
#
#From the Producer perspective, in the autogenerated producer-side test:
#
#(1) - A request will be sent to the producer
#(2) - With the "PUT" method
#(3) - to the URL "/fraudcheck"
#(4) - with the JSON body that
# * has a field `client.id` `1234567890`
# * has a field `loanAmount` that is equal to `99999`
#(5) - with header `Content-Type` equal to `application/json`
#(7) - then the test will assert if the response has been sent with
#(8) - status equal `200`
#(9) - and JSON body equal to
# { "fraudCheckStatus": "FRAUD", "rejectionReason": "Amount too high" }
#(10) - with header `Content-Type` equal to `application/json;charset=UTF-8`

The YML contract is quite straight-forward. However when you take a look at the Contract written using a statically typed Groovy DSL - you might wonder what the value(client(…​), server(…​)) parts are. By using this notation, Spring Cloud Contract lets you define parts of a JSON block, a URL, etc., which are dynamic. In case of an identifier or a timestamp, you need not hardcode a value. You want to allow some different ranges of values. To enable ranges of values, you can set regular expressions matching those values for the consumer side. You can provide the body by means of either a map notation or String with interpolations. Consult the docs for more information. We highly recommend using the map notation!

	Tip
	You must understand the map notation in order to set up contracts. Please read the Groovy docs regarding JSON.

The previously shown contract is an agreement between two sides that:

Once you are ready to check the API in practice in the integration tests, you need to install the stubs locally.

Add the Spring Cloud Contract Verifier plugin.

We can add either a Maven or a Gradle plugin. In this example, you see how to add Maven. First, add the Spring Cloud Contract BOM.

<dependencyManagement>
	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-dependencies</artifactId>
			<version>${spring-cloud-dependencies.version}</version>
			<type>pom</type>
			<scope>import</scope>
		</dependency>
	</dependencies>
</dependencyManagement>

Next, add the Spring Cloud Contract Verifier Maven plugin

<plugin>
	<groupId>org.springframework.cloud</groupId>
	<artifactId>spring-cloud-contract-maven-plugin</artifactId>
	<version>${spring-cloud-contract.version}</version>
	<extensions>true</extensions>
	<configuration>
		<packageWithBaseClasses>com.example.fraud</packageWithBaseClasses>
	</configuration>
</plugin>

Since the plugin was added, you get the Spring Cloud Contract Verifier features which, from the provided contracts:

You do not want to generate tests since you, as the consumer, want only to play with the stubs. You need to skip the test generation and execution. When you execute:

$ cd local-http-server-repo
$ ./mvnw clean install -DskipTests

In the logs, you see something like this:

[INFO] --- spring-cloud-contract-maven-plugin:1.0.0.BUILD-SNAPSHOT:generateStubs (default-generateStubs) @ http-server ---
[INFO] Building jar: /some/path/http-server/target/http-server-0.0.1-SNAPSHOT-stubs.jar
[INFO]
[INFO] --- maven-jar-plugin:2.6:jar (default-jar) @ http-server ---
[INFO] Building jar: /some/path/http-server/target/http-server-0.0.1-SNAPSHOT.jar
[INFO]
[INFO] --- spring-boot-maven-plugin:1.5.5.BUILD-SNAPSHOT:repackage (default) @ http-server ---
[INFO]
[INFO] --- maven-install-plugin:2.5.2:install (default-install) @ http-server ---
[INFO] Installing /some/path/http-server/target/http-server-0.0.1-SNAPSHOT.jar to /path/to/your/.m2/repository/com/example/http-server/0.0.1-SNAPSHOT/http-server-0.0.1-SNAPSHOT.jar
[INFO] Installing /some/path/http-server/pom.xml to /path/to/your/.m2/repository/com/example/http-server/0.0.1-SNAPSHOT/http-server-0.0.1-SNAPSHOT.pom
[INFO] Installing /some/path/http-server/target/http-server-0.0.1-SNAPSHOT-stubs.jar to /path/to/your/.m2/repository/com/example/http-server/0.0.1-SNAPSHOT/http-server-0.0.1-SNAPSHOT-stubs.jar

The following line is extremely important:

[INFO] Installing /some/path/http-server/target/http-server-0.0.1-SNAPSHOT-stubs.jar to /path/to/your/.m2/repository/com/example/http-server/0.0.1-SNAPSHOT/http-server-0.0.1-SNAPSHOT-stubs.jar

It confirms that the stubs of the http-server have been installed in the local repository.

Run the integration tests.

In order to profit from the Spring Cloud Contract Stub Runner functionality of automatic stub downloading, you must do the following in your consumer side project (Loan Application service):

Add the Spring Cloud Contract BOM:

<dependencyManagement>
	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-dependencies</artifactId>
			<version>${spring-cloud-dependencies.version}</version>
			<type>pom</type>
			<scope>import</scope>
		</dependency>
	</dependencies>
</dependencyManagement>

Add the dependency to Spring Cloud Contract Stub Runner:

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

Annotate your test class with @AutoConfigureStubRunner. In the annotation, provide the group-id and artifact-id for the Stub Runner to download the stubs of your collaborators. (Optional step) Because you’re playing with the collaborators offline, you can also provide the offline work switch.

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment=WebEnvironment.NONE)
@AutoConfigureStubRunner(ids = {"com.example:http-server-dsl:+:stubs:6565"}, workOffline = true)
public class LoanApplicationServiceTests {

Now, when you run your tests, you see something like this:

2016-07-19 14:22:25.403  INFO 41050 --- [           main] o.s.c.c.stubrunner.AetherStubDownloader  : Desired version is + - will try to resolve the latest version
2016-07-19 14:22:25.438  INFO 41050 --- [           main] o.s.c.c.stubrunner.AetherStubDownloader  : Resolved version is 0.0.1-SNAPSHOT
2016-07-19 14:22:25.439  INFO 41050 --- [           main] o.s.c.c.stubrunner.AetherStubDownloader  : Resolving artifact com.example:http-server:jar:stubs:0.0.1-SNAPSHOT using remote repositories []
2016-07-19 14:22:25.451  INFO 41050 --- [           main] o.s.c.c.stubrunner.AetherStubDownloader  : Resolved artifact com.example:http-server:jar:stubs:0.0.1-SNAPSHOT to /path/to/your/.m2/repository/com/example/http-server/0.0.1-SNAPSHOT/http-server-0.0.1-SNAPSHOT-stubs.jar
2016-07-19 14:22:25.465  INFO 41050 --- [           main] o.s.c.c.stubrunner.AetherStubDownloader  : Unpacking stub from JAR [URI: file:/path/to/your/.m2/repository/com/example/http-server/0.0.1-SNAPSHOT/http-server-0.0.1-SNAPSHOT-stubs.jar]
2016-07-19 14:22:25.475  INFO 41050 --- [           main] o.s.c.c.stubrunner.AetherStubDownloader  : Unpacked file to [/var/folders/0p/xwq47sq106x1_g3dtv6qfm940000gq/T/contracts100276532569594265]
2016-07-19 14:22:27.737  INFO 41050 --- [           main] o.s.c.c.stubrunner.StubRunnerExecutor    : All stubs are now running RunningStubs [namesAndPorts={com.example:http-server:0.0.1-SNAPSHOT:stubs=8080}]

This output means that Stub Runner has found your stubs and started a server for your app with group id com.example, artifact id http-server with version 0.0.1-SNAPSHOT of the stubs and with stubs classifier on port 8080.

File a pull request.

What you have done until now is an iterative process. You can play around with the contract, install it locally, and work on the consumer side until the contract works as you wish.

Once you are satisfied with the results and the test passes, publish a pull request to the server side. Currently, the consumer side work is done.

As a developer of the Fraud Detection server (a server to the Loan Issuance service):

Create an initial implementation.

As a reminder, you can see the initial implementation here:

@RequestMapping(value = "/fraudcheck", method = PUT)
public FraudCheckResult fraudCheck(@RequestBody FraudCheck fraudCheck) {
return new FraudCheckResult(FraudCheckStatus.OK, NO_REASON);
}

Take over the pull request.

$ git checkout -b contract-change-pr master
$ git pull https://your-git-server.com/server-side-fork.git contract-change-pr

You must add the dependencies needed by the autogenerated tests:

<dependency>
	<groupId>org.springframework.cloud</groupId>
	<artifactId>spring-cloud-starter-contract-verifier</artifactId>
	<scope>test</scope>
</dependency>

In the configuration of the Maven plugin, pass the packageWithBaseClasses property

<plugin>
	<groupId>org.springframework.cloud</groupId>
	<artifactId>spring-cloud-contract-maven-plugin</artifactId>
	<version>${spring-cloud-contract.version}</version>
	<extensions>true</extensions>
	<configuration>
		<packageWithBaseClasses>com.example.fraud</packageWithBaseClasses>
	</configuration>
</plugin>

Important

This example uses "convention based" naming by setting the packageWithBaseClasses property. Doing so means that the two last packages combine to make the name of the base test class. In our case, the contracts were placed under src/test/resources/contracts/fraud. Since you do not have two packages starting from the contracts folder, pick only one, which should be fraud. Add the Base suffix and capitalize fraud. That gives you the FraudBase test class name.

All the generated tests extend that class. Over there, you can set up your Spring Context or whatever is necessary. In this case, use Rest Assured MVC to start the server side FraudDetectionController.

package com.example.fraud;

import org.junit.Before;

import io.restassured.module.mockmvc.RestAssuredMockMvc;

public class FraudBase {
	@Before
	public void setup() {
		RestAssuredMockMvc.standaloneSetup(new FraudDetectionController(),
				new FraudStatsController(stubbedStatsProvider()));
	}

	private StatsProvider stubbedStatsProvider() {
		return fraudType -> {
			switch (fraudType) {
			case DRUNKS:
				return 100;
			case ALL:
				return 200;
			}
			return 0;
		};
	}

	public void assertThatRejectionReasonIsNull(Object rejectionReason) {
		assert rejectionReason == null;
	}
}

Now, if you run the ./mvnw clean install, you get something like this:

Results :

Tests in error:
  ContractVerifierTest.validate_shouldMarkClientAsFraud:32 » IllegalState Parsed...

This error occurs because you have a new contract from which a test was generated and it failed since you have not implemented the feature. The auto-generated test would look like this:

@Test
public void validate_shouldMarkClientAsFraud() throws Exception {
    // given:
        MockMvcRequestSpecification request = given()
                .header("Content-Type", "application/vnd.fraud.v1+json")
                .body("{\"client.id\":\"1234567890\",\"loanAmount\":99999}");

    // when:
        ResponseOptions response = given().spec(request)
                .put("/fraudcheck");

    // then:
        assertThat(response.statusCode()).isEqualTo(200);
        assertThat(response.header("Content-Type")).matches("application/vnd.fraud.v1.json.*");
    // and:
        DocumentContext parsedJson = JsonPath.parse(response.getBody().asString());
        assertThatJson(parsedJson).field("['fraudCheckStatus']").matches("[A-Z]{5}");
        assertThatJson(parsedJson).field("['rejection.reason']").isEqualTo("Amount too high");
}

If you used the Groovy DSL, you can see, all the producer() parts of the Contract that were present in the value(consumer(…​), producer(…​)) blocks got injected into the test. In case of using YAML, the same applied for the matchers sections of the response.

Note that, on the producer side, you are also doing TDD. The expectations are expressed in the form of a test. This test sends a request to our own application with the URL, headers, and body defined in the contract. It also is expecting precisely defined values in the response. In other words, you have the red part of red, green, and refactor. It is time to convert the red into the green.

Write the missing implementation.

Because you know the expected input and expected output, you can write the missing implementation:

@RequestMapping(value = "/fraudcheck", method = PUT)
public FraudCheckResult fraudCheck(@RequestBody FraudCheck fraudCheck) {
if (amountGreaterThanThreshold(fraudCheck)) {
	return new FraudCheckResult(FraudCheckStatus.FRAUD, AMOUNT_TOO_HIGH);
}
return new FraudCheckResult(FraudCheckStatus.OK, NO_REASON);
}

When you execute ./mvnw clean install again, the tests pass. Since the Spring Cloud Contract Verifier plugin adds the tests to the generated-test-sources, you can actually run those tests from your IDE.

Deploy your app.

Once you finish your work, you can deploy your change. First, merge the branch:

$ git checkout master
$ git merge --no-ff contract-change-pr
$ git push origin master

Your CI might run something like ./mvnw clean deploy, which would publish both the application and the stub artifacts.

As a developer of the Loan Issuance service (a consumer of the Fraud Detection server):

Merge branch to master.

$ git checkout master
$ git merge --no-ff contract-change-pr

Work online.

Now you can disable the offline work for Spring Cloud Contract Stub Runner and indicate where the repository with your stubs is located. At this moment the stubs of the server side are automatically downloaded from Nexus/Artifactory. You can switch off the value of the workOffline parameter in your annotation. The following code shows an example of achieving the same thing by changing the properties.

stubrunner:
  ids: 'com.example:http-server-dsl:+:stubs:8080'
  repositoryRoot: https://repo.spring.io/libs-snapshot

That’s it!

You can check out the video from the Warsaw JUG about Spring Cloud Contract: