2. Spring Cloud Contract Verifier Introduction
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# 2. Spring Cloud Contract Verifier Introduction

| Tip
The Accurest project was initially started by Marcin Grzejszczak and Jakub Kubrynski (codearte.io)

Just to make long story short - Spring Cloud Contract Verifier is a tool that enables Consumer Driven Contract (CDC) development of JVM-based applications. It is shipped with Contract Definition Language (DSL). Contract definitions are used to produce following resources:

- JSON stub definitions to be used by WireMock when doing integration testing on the client code (client tests). Test code must still be written by hand, test data is produced by Spring Cloud Contract Verifier.
- Messaging routes if you’re using one. We’re integrating with Spring Integration, Spring Cloud Stream, Spring AMQP and Apache Camel. You can however set your own integrations if you want to
- Acceptance tests (in JUnit or Spock) used to verify if server-side implementation of the API is compliant with the contract (server tests). Full test is generated by Spring Cloud Contract Verifier.

Spring Cloud Contract Verifier moves TDD to the level of software architecture.

## 2.1 Why?

Let us assume that we have a system comprising of multiple microservices:

### 2.1.1 Testing issues

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

- deploy all microservices and perform end to end tests
- mock other microservices in unit / integration tests

Both have their advantages but also a lot of disadvantages. Let’s focus on the latter.

Deploy all microservices and perform end to end tests

Advantages:

- simulates production
- tests real communication between services

Disadvantages:

- to test one microservice we would have to deploy 6 microservices, a couple of databases etc.
- the environment where the tests would be conducted would be locked for a single suite of tests (i.e. nobody else would be able to run the tests in the meantime).
- long to run
- very late feedback
- extremely hard to debug

Mock other microservices in unit / integration tests

Advantages:

- very fast feedback
- no infrastructure requirements

Disadvantages:

- the implementor of the service creates stubs thus they might have nothing to do with the reality
- you can go to production with passing tests and failing production

To solve the aforementioned issues Spring Cloud Contract Verifier with Stub Runner were created. Their 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 is using directly.

Spring Cloud Contract Verifier gives you the certainty that the stubs that you’re using 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 other words - you can trust those stubs.

## 2.2 Purposes

The main purposes of Spring Cloud Contract Verifier with Stub Runner are:

- to ensure that WireMock / Messaging stubs (used when developing the client) are doing exactly what actual server-side implementation will do,
- to promote ATDD method and Microservices architectural style,
- to provide a way to publish changes in contracts that are immediately visible on both sides,
- to generate boilerplate test code used on the server side.

| Important
Spring Cloud Contract Verifier’s purpose is NOT to start writing business features in the contracts. Let’s assume that we have a business use case of fraud check. If a user can be a fraud for 100 different reasons, we would assume that you would create 2 contracts. One for the positive and one for the negative fraud case. Contract tests are used to test contracts between applications and not to simulate full behaviour.

## 2.3 How

### 2.3.1 Define the contract

As consumers we need to define what exactly we want to achieve. We need to formulate our expectations. That’s why we write the following contract.

Let’s assume that we’d like to send the request containing the id of the client and the amount he wants to borrow from us. We’d like to send it to the /fraudcheck url via the PUT method.

    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 OK() // (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.*`
     */

### 2.3.2 Client Side

Spring Cloud Contract will generate stubs, which you can use during client side testing. You will have a WireMock instance / Messaging route up and running that simulates the service Y. 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"},
    		stubsMode = StubRunnerProperties.StubsMode.LOCAL)
    @DirtiesContext
    public class LoanApplicationServiceTests {

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

### 2.3.3 Server Side

Being a service Y since you are developing your stub, you need to be sure that it’s actually resembling your concrete implementation. You can’t have a situation where your stub acts in one way and your application on production behaves in a different way.

That’s why from the provided stub acceptance tests will be generated that will ensure that your application behaves in the same way as you define in your stub.

The autogenerated 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");
    }

## 2.4 Step by step guide to CDC

Let’s take an example of Fraud Detection and Loan Issuance process. The business scenario is such that we want to issue loans to people but don’t want them to steal the money from us. The current implementation of our system grants loans to everybody.

Let’s assume that the `Loan Issuance` is a client to the `Fraud Detection` server. In the current sprint we are required to develop a new feature - if a client wants to borrow too much money then we mark him as fraud.

Technical remark - Fraud Detection will have artifact id `http-server`, Loan Issuance `http-client` and both have group id `com.example`.

Social remark - both client and server development teams need to communicate directly and discuss changes while going through the process. CDC is all about communication.

The server side code is available here and the client side code here.

| Tip
In this case the ownership of the contracts lays on the producer side. It means that physically all the contract are present in the producer’s repository

### 2.4.1 Technical note

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

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" }
    }

### 2.4.2 Consumer side (Loan Issuance)

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

start doing TDD by writing a test to 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");
    }

We’ve just written a test of our new feature. If a loan application for a big amount is received we 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. Let’s assume that we’d like to send the request containing the id of the client and the amount he wants to borrow from us. We’d like 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 we’ve hardcoded the port of the Fraud Detection service at `8080` and our application is running on `8090`.

If we’d start the written test it would obviously break since we have no service running on port `8080`.

clone the Fraud Detection service repository locally

We’ll start playing around with the server side contract. That’s why we need to 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 consumers we need to define what exactly we want to achieve. We need to formulate our expectations. That’s why we write the following contract.

| Important
We’re placing the contract under `src/test/resources/contracts/fraud` folder. The `fraud` folder is important cause we’ll reference that folder in the producer’s test base class name.

    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 OK() // (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.*`
     */

The Contract is written using a statically typed Groovy DSL. You might be wondering what are those `value(client(…​), server(…​))` parts. By using this notation Spring Cloud Contract allows you to define parts of a JSON / URL / etc. which are dynamic. In case of an identifier or a timestamp you don’t want to hardcode a value. You want to allow some different ranges of values. That’s why for the consumer side you can set regular expressions matching those values. You can provide the body either by means of a map notation or String with interpolations. Consult the docs for more information. We highly recommend using the map notation!

| Tip
It’s really important that you understand the map notation to set up contracts. Please read the Groovy docs regarding JSON

The aforementioned contract is an agreement between two sides that:

- if an HTTP request is sent with

  - a method `PUT` on an endpoint `/fraudcheck`
  - JSON body with `client.id` matching the regular expression `[0-9]{10}` and `loanAmount` equal to `99999`
  - and with a header `Content-Type` equal to `application/vnd.fraud.v1+json`

- then an HTTP response would be sent to the consumer that

  - has status `200`
  - contains JSON body with the `fraudCheckStatus` field containing a value `FRAUD` and the `rejectionReason` field having value `Amount too high`
  - and a `Content-Type` header with a value of `application/vnd.fraud.v1+json`

Once we’re ready to check the API in practice in the integration tests we need to just install the stubs locally

add the Spring Cloud Contract Verifier plugin

We can add either Maven or Gradle plugin - in this example we’ll show how to add Maven. First we need to 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, 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 we get the `Spring Cloud Contract Verifier` features which from the provided contracts:

- generate and run tests
- produce and install stubs

We don’t want to generate tests since we, as consumers, want only to play with the stubs. That’s why we need to skip the tests generation and execution. When we execute:

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

In the logs we’ll 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:1.5.4.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

This 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’s confirming 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 have to do the following in our 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 stubs of your collaborators. Also provide the offline work switch since you’re playing with the collaborators offline (optional step).

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

Now if you run your tests you’ll see sth 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}]

Which means that Stub Runner has found your stubs and started a server for 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 PR

What we did until now is an iterative process. We can play around with the contract, install it locally and work on the consumer side until we’re happy with the contract.

Once we’re satisfied with the results and the test passes publish a PR to the server side. Currently the consumer side work is done.

### 2.4.3 Producer side (Fraud Detection server)

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

initial implementation

As a reminder here you can see the initial implementation

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

take over the PR

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

You have to 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 we passed 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
We’ve decided to use the "convention based" naming by setting the `packageWithBaseClasses` property. That means that 2 last packages will be combined into a name of the base test class. In our case the contracts were placed under `src/test/resources/contracts/fraud`. Since we don’t have 2 packages starting from the `contracts` folder we’re picking only one which is `fraud`. We’re adding the `Base` suffix and we’re capitalizing `fraud`. That gives us the `FraudBase` test class name.

That’s because all the generated tests will extend that class. Over there you can set up your Spring Context or whatever is necessary. In our case we’re using 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 would get sth like this:

    Results :

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

That’s because you have a new contract from which a test was generated and it failed since you haven’t implemented the feature. The autogenerated 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");
    }

As you can see all the `producer()` parts of the Contract that were present in the `value(consumer(…​), producer(…​))` blocks got injected into the test.

What’s important here to note is that on the producer side we also are doing TDD. We have expectations in form of a test. This test is shooting a request to our own application to an URL, headers and body defined in the contract. It also is expecting very precisely defined values in the response. In other words you have is your `red` part of `red`, `green` and `refactor`. Time to convert the `red` into the `green`.

write the missing implementation

Now since we now what is the expected input and expected output let’s 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);
    }

If we execute `./mvnw clean install` again the tests will 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’ve finished your work it’s time to deploy your change. First merge the branch

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

Then we assume that your CI would run sth like `./mvnw clean deploy` which would publish both the application and the stub artifcats.

### 2.4.4 Consumer side (Loan Issuance) final step

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 provide where the repository with your stubs is placed. At this moment the stubs of the server side will be automatically downloaded from Nexus / Artifactory. You can switch off the value of the `workOffline` parameter in your annotation. Below you can see an example of achieving the same by changing the properties.

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

And that’s it!

## 2.5 Dependencies

The best way to add the dependencies is to just use the proper `starter` dependency.

For `stub-runner` use `spring-cloud-starter-stub-runner` and when you’re using a plugin just add `spring-cloud-starter-contract-verifier`.

## 2.6 Additional links

Below you can find some resources related to Spring Cloud Contract Verifier and Stub Runner. Note that some can be outdated since the Spring Cloud Contract Verifier project is under constant development.

### 2.6.1 Spring Cloud Contract video

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

### 2.6.2 Readings

- Slides from Marcin Grzejszczak’s talk about Accurest
- Accurest related articles from Marcin Grzejszczak’s blog
- Spring Cloud Contract related articles from Marcin Grzejszczak’s blog
- Groovy docs regarding JSON

## 2.7 Samples

Here you can find some samples.

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