Stick to the rules - Consumer Driven Contracts. 2015.07 Confitura

Stick to the rules!
Consumer Driven Contracts
04.07.2015 - Confitura PL
Marcin Grzejszczak @mgrzejszczak

@confiturapl @mgrzejszczak / @4financeit
Swim for a dream
http://swimforadream.com/
Adam will swim 18.5 km from Hel to Gdynia
Money for 3 charity organizations

Marcin Grzejszczak
● Software Architect at 4financeIT
● Author of "Mockito Instant", "Mockito Cookbook"
● Co-author of "micro-infra-spring",
“spring-cloud-zookeeper”, “spring-cloud-sleuth”
Twitter: @MGrzejszczak
Blog: http://toomuchcoding.blogspot.com
Homepage: http://marcin.grzejszczak.pl

Agenda
● Short introduction
● Real life scenario with a hilarious joke
● How does it work?
● Live (hopefully) coding
● Summary

Consumer Driven Contracts
● TDD on architectural level
○ mistakes occur both in implementation and design
● Try to use API before implementing it

Real life scenario...

Hi! I’m team
X and we
have spent
weeks to
tweak our
code to use
your API!

That’s so
sweet… But
we’ve just
changed our
API because
well, it’s ours.

You’ve got to
be shitting
me! (however
it sounds)

CDC building blocks
● Server
● Consumer
● Contract

CDC building blocks

How to make life easier?
Use common contract

Contract definition

What is a contract?
io.codearte.accurest.dsl.GroovyDsl.make {
request {
method "PUT"
url "/fraudcheck"
body(''' { “clientPesel":"12345678901", "loanAmount":123.123 } ''' )
headers { header("Content-Type", "application/fraud+json") }
}
response {
status 200
body( """{ "fraudCheckStatus": "OK"}""")
headers { header('Content-Type': 'application/fraud+json') }
}
}

What is a contract?
request {
method "PUT"
url "/fraudcheck"
}
response {
status 200
}
}
Groovy DSL

What is a contract?
request {
method "PUT"
url "/fraudcheck"
}
response {
status 200
}
}
FOR A GIVEN
REQUEST

What is a contract?
request {
method "PUT"
url "/fraudcheck"
}
response {
status 200
}
}
WE’LL HAVE SUCH A
RESPONSE

So how am I supposed to work?

Workflow - Consumer side
CLONE SERVER REPO
AND WORK OFFLINE

1) ALTER THE CONTRACT LOCALLY
2) GENERATE AND COPY STUBS
3) USE STUBS IN CONSUMER TESTS

What is a stub?
● JSON representation of a Groovy DSL contract
● Understood by Wiremock Http Server Stub

FILE A PULL REQUEST WITH
THE PROPOSED CONTRACT

Server tests - what happens there?
● server has DSLs with contracts
● tests are generated from the contracts
● stubs that consumers can use are
generated from the contracts

Workflow - Server side
● oh, I have a PR with the proposed contract
● I don’t have the implementation ready so
my generated tests are failing
● I’ll add the implementation, fix the tests
and merge the PR!

Workflow - Server side
IMPLEMENTATION IS READY
I’LL PUBLISH MY STUB!

Consumer Technology
Wiremock
http://wiremock.org
testCompile 'com.github.tomakehurst:wiremock:1.56'
{
"request": {
"method": "GET",
"url": "/hello"
},
"response": {
"status": 200,
"body": "Hello world!",
"headers": { "Content-Type": "text/plain" }
}
}
Configuration
Sample definition

Server Technology
Accurate REST
https://github.com/Codearte/accurest
buildscript {
repositories {
mavenCentral()
}
dependencies {
classpath 'io.codearte.accurest:accurest-gradle-plugin:0.7.0'
}
}
apply plugin: 'accurest'

Example

New feature

Let consumer drive the contract!

Live coding - consumer side

Consumer prepared the contract
request {
method "PUT"
url "/fraudcheck"
body(''' { “clientPesel":"1234567890", "loanAmount":99999 } ''' )
headers { header("Content-Type", "application/vnd.fraud.v1+json") }
}
response {
status 200
body( """{ "fraudCheckStatus": "REJECTED", "rejectionReason": "Amount too high" }""")
headers { header('Content-Type': 'application/vnd.fraud.v1+json') }
}
}

Time for server side implementation!

Live coding - server side

CDC benefits

CDC benefits
● Rapid API prototyping
● Non-blocking development
● Behaviour Driven Development

CDC benefits
● Client tells what he needs
● Quality - continuously checking if contract
is valid

CDC benefits
● if server breaks API compatibility
consumer tests fail
● if server adds new API I can reuse it
immediately in my tests

CDC benefits
● The server tests are generated for you
● Any typos / misunderstandings will be found
out immediately

Not so fast...
● Maintaining datasets
● What exactly to verify for server side?
● Breaking changes
● Accurest under development
○ I also have to sleep sometimes

Q&A
https://github.com/marcingrzejszczak/2015_confitura_cdc
Accurest: https://github.com/Codearte/accurest
Micro-Infra-Spring: https://github.com/4finance/micro-infra-spring
CDC: http://martinfowler.com/articles/consumerDrivenContracts.html

Stick to the rules - Consumer Driven Contracts. 2015.07 Confitura

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