Creating a Rest API is simple these days. To be able to change your API and still keep it working for all consumers is much harder. When using Consumer Contracts, you can let your API evolve and verify you can still uphold the contract of your consumers. In this presentation I will be demonstrating this by using Spring Cloud Contract.

1. Consumer Driven Contract Testing
Mike van Vendeloo @mikevanvendeloo

2. @mikevanvendeloo
About me
Mike van Vendeloo
Software Craftsman
Scrum Master
Focussed on software quality and automation

3. @mikevanvendeloo
Agenda
1. Background
2. Consumer Driven Contract Testing
3. Spring Cloud Contract

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Consumer Driven Contracts to the rescue
Consumer Driven Contracts is a pattern that drives the
development of the Producer from its Consumers point of view.

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Terminology
A Contract is a collection of agreements between a client
(Consumer) and an API (Producer) that describes the
interactions that can take place between them.
Consumer: Service listening to messages or requesting API methods
Producer: Service sending messages or exposing an API
Contract: Agreement between producer and consumer how the API (method,
request and response) / message will look like

11. @mikevanvendeloo
Technology Radar
“The concept isn’t new, but with the mainstream
acceptance of microservices, we need to remind
people that consumer-driven contracts are an
essential part of a mature microservice testing
portfolio, enabling independent service
deployments.”

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Consumer Driven Contract Testing
“TDD on the architectural level”
“Use an API before implementing it”
-- Marcin Grzejszczak --

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Frameworks
Pact - https://docs.pact.io/
Pact-JVM - https://github.com/DiUS/pact-jvm
Karma-Pact - https://github.com/pact-foundation/karma-pact
Pacto - http://thoughtworks.github.io/pacto/
AccuRest - https://github.com/Codearte/accurest -> Spring Cloud Contract
And many more...

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Consumer
Spring Cloud Contract
Producer
A
P
I
Consumer

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Spring Cloud Contract
● Spring Cloud Contract Verifier
● Spring Cloud Contract Wiremock
● Spring Cloud Contract Stubrunner

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Contract DSL
package net.vanvendeloo.demos.comicbooks
org.springframework.cloud.contract.spec.Contract.make {
description(“”” Some explanation in given/when/then style “””)
request {
method 'PUT'
url '/comicbook'
body ([ title : ‘Game of drones’, isbn: ‘9789002259722’])
}
response {
status 201
}
}

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Contract
verifier tests
Producer side
Maven
repository
stubs.jar
contract
Producer
A
P
I
generate
generate

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You can easily compile Contracts to WireMock stubs mapping using standalone maven
command:
mvn org.springframework.cloud:spring-cloud-contract-maven-plugin:convert
Producer side - Wiremock

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{
"id" : "2656c2c0-64b1-4d54-8ccd-8b5db4304248",
"request" : {
"url" : "/comics",
"method" : "GET"
},
"response" : {
"status" : 200,
"body" : "[{"id":1,"name":"Suske en Wiske","comicBooks":[{"id":1,"title":"Game of
drones","isbn":"9789002259722","number":337}]}]",
"headers" : {
"Content-Type" : "application/json"
},
"transformers" : [ "response-template" ]
},
"uuid" : "2656c2c0-64b1-4d54-8ccd-8b5db4304248"
}
Producer side - Stubs

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<plugin>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-contract-maven-plugin</artifactId>
<version>${spring-cloud-contract.version}</version>
<extensions>true</extensions>
<configuration>
<packageWithBaseClasses>net.vanvendeloo.demo.comicbooks</packageWi
thBaseClasses>
</configuration>
</plugin>
Producer side - Generate tests and stubs

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package net.vanvendeloo.demo.cloudcontract.comiccollection;
import org.junit.Before;
import com.jayway.restassured.module.mockmvc.RestAssuredMockMvc;
public class ComicCollectionTestBase {
@Before
public void setup() {
RestAssuredMockMvc.standaloneSetup(new ComicCollectionController());
}
}
Producer side - Base class

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Consumer side
Maven
repository
stubs.jar
Consumer
Stub
runner
T
E
S
T
S
download

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Consumer side - Using stubs (1)
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-contract-stub-runner</artifactId>
<scope>test</scope>
</dependency>

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@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment=WebEnvironment.NONE)
@AutoConfigureStubRunner(ids =
{"net.vanvendeloo.demo.comicbooks:comic-collections-api:+:stubs:8090"
}, workOffline = true)
@DirtiesContext
public class ComicCollectionApplicationTest {
…
}
Consumer side - Using stubs (2)

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Advanced contracts - Regular expressions
org.springframework.cloud.contract.spec.Contract.make {
request {
method 'POST'
url '/comicbook/1'
headers { contentType(applicationJson()) }
body(
title: $(consumer(regex(‘[A-Za-z ]+)), producer('My title')),
isbn: $(consumer(regex('[0-9]{10}')), producer('1234567890'))
)
}
...

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Set properties in the body
value(consumer(...), producer(...))
$(consumer(...), producer(...))
Reuse of request information in the response
fromRequest().body(String jsonPath)
Advanced contracts - Dynamic properties

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Test matchers
jsonPath('$.isbn', byRegex(number()))
jsonPath('$.returned', byRegex(anyBoolean()))
jsonPath('$.returndate, byRegex(byDate()))
Results in testcode
assertThat(parsedJson.read("$.isbn", String.class)).matches("-?d*(.d+)?");
assertThat(parsedJson.read("$.returned", String.class)).matches("(true|false)");
assertThat(parsedJson.read("$.returndate",
String.class)).matches("(dddd)-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01])");
Advanced contracts - Test matchers

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Ability to specify how the dynamic values should be generated by wiremock
jsonPath('$.isbn, byRegex(number()))
jsonPath('$.returned, byRegex(anyBoolean()))
jsonPath('$.returnDate, byDate())
{ "matchesJsonPath" : "$[?(@.isbn =~ /(-?d*(.d+)?)/)]"},
{ "matchesJsonPath" : "$[?(@.returned =~ /((true|false))/)]"},
{ "matchesJsonPath" : "$[?(@.returndate =~
/((dddd)-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01]))/)]"}
Advanced contracts - Stub matchers

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this.mockMvc.perform(post("/comicbooksearch")
.accept(MediaType.APPLICATION_JSON)
.contentType(MediaType.APPLICATION_JSON)
.content("{"number": 337 }"))
.andExpect(status().isOk())
.contentType(MediaType.valueOf("application/json"))
.stub("shouldReturnComicBook"))
// then Contract DSL documentation
.andDo(document("getComicBook",
SpringCloudContractRestDocs.dslContract()));
Advanced contracts - Generate from RestDocs

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Contract Repository
Sharing the contracts via a separate repository
<plugin>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-contract-maven-plugin</artifactId>
<configuration>
<contractsRepositoryUrl>http://link/to/your/nexus</contractsRepositoryUrl>
<contractDependency>
<groupId>net.vanvendeloo.demos.comiccollections</groupId>
<artifactId>contracts</artifactId>
</contractDependency>
</configuration>
</plugin>

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Contract Testing with messaging
Out of the box integration for using stubs with the following frameworks
● Spring Integration
● Spring Cloud Stream
● Apache Camel
● Spring AMQP

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Contract.make {
label 'return_comicbook_1'
input {
triggeredBy('bookReturnedTriggered()')
}
outputMessage {
sentTo('returnBook')
body('''{ "title" : "Game of drones" }''')
headers {
header('TITLE', 'Game of drones')
}
}
}
Contract for messages

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Conclusions
● Communication is still the most important thing!
● CDC frameworks are still in development
● Spring Cloud Contract
○ integrates well with the Spring ecosystem
○ ensures reusable stubs
○ in the future, will provide improved tooling for non-Java
users

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References
https://martinfowler.com/articles/consumerDrivenContracts.html
https://github.com/spring-cloud-samples/spring-cloud-contract-samples
https://www.youtube.com/watch?v=sAAklvxmPmk&t=547s