Service integration can be a pain when providers of APIs don't have visibility into how they're being consumed. Evolving their APIs can be a slow, painful process. When a contract breaking change is released, API consumers may not find out until in production, which integration point failed and why. Contract Tests are lightweight, easy to maintain, and quick at detecting breaking changes in API contracts. Even better are Consumer-Driven Contract Tests (CDCTs), that help consumers build their integrations based on provider contracts they expect. Serving these contracts to providers enable their creators evolve their APIs while complying with consumers' specifications.

1. Pain Free Microservices
Integration
Using Contract Tests With Pact
Ama Asare & Danilo Sato

2. Some context
● Microservices architecture
● Agile environment
● Collaboration between teams

3. Usual problem
● How to test all components work together?
● How to evolve an API with confidence?

4. Usual solution
● Fully integrated tests:
៙ Slow
៙ Hard to maintain
៙ Lots of infrastructure
៙ Hard to fix issues (which part failed?)

5. Unit tests at system boundaries?
● Make assumptions about collaborators
● Test your item of interest with those assumptions
System A
Mock
System B
System A
Actual
System B

6. A step further
System A
Actual
System B
record

7. Two steps further
System A
record
assume B
Actual
System Bverify
Mock
System A

8. Why do you need
Contract Tests?

9. Why
● Fast Feedback
៙ Detect breaking API changes early
៙ Detect what broke quickly
● Confidence to Deploy
៙ Decouple deployments

10. Why
● Enables Consumer-Driven Contract Testing
៙ TDD at a higher level!
៙ Can develop consumers before providers
៙ Providers implement only what’s needed

11. How to implement?
With Pact

12. JS Consumer - Setup

13. JS Consumer - Arrange

14. JS Consumer - Act and Assert

15. Pact File (JSON)
Consumer assumes...

16. Java Provider - Verify (Gradle)

17. How to share contracts?
Using Pact Broker!

18. Pact Broker

19. Pact Broker

20. Java Provider - Verify (Gradle)

21. How to integrate into
the pipeline?

22. Consumer Pipeline
Commit PackageTest
Unit Test
Contract
Test
Functional
Test
Tag with
“prod”
Publish
Deploy to
Dev
Deploy to
QA
Deploy to
Prod
Publish
Contract
Tag with
“dev”
Tag with
“qa”

23. Provider Pipeline
Commit PackageTest
Unit Test
Verify
Contract
Functional
Test
Verify
Contract
Publish
Deploy to
Dev
Deploy to
QA
Deploy to
Prod
Verify
Contract
Verify
Contract
➔ ➔ ➔ ➔LATEST QADEV PROD

24. {
“age”: 5,
“name”: “John Doe”
}
{
“age”: 5,
“name”: “John Doe”,
“firstName”: “John”,
“lastName”: “Doe”
}
{
“age”: 5,
“firstName”: “John”,
“lastName”: “Doe”
}
PROVIDER v1 v2 v3

25. {
“age”: 5,
“name”: “John Doe”
}
{
“age”: 5,
“name”: “John Doe”,
“firstName”: “John”,
“lastName”: “Doe”
}
{
“age”: 5,
“firstName”: “John”,
“lastName”: “Doe”
}
PROVIDER v1 v2 v3
LATEST QADEV PRODUCTION
PROVIDER
CONSUMER A
(age, name)
CONSUMER B
(age)

26. {
“age”: 5,
“name”: “John Doe”
}
{
“age”: 5,
“name”: “John Doe”,
“firstName”: “John”,
“lastName”: “Doe”
}
{
“age”: 5,
“firstName”: “John”,
“lastName”: “Doe”
}
PROVIDER v1 v2 v3
LATEST QADEV PRODUCTION
v2 v2v2 v2PROVIDER
v2 v1v2 v1CONSUMER A
(age, name)
v1 v1v1 v1CONSUMER B
(age)

27. {
“age”: 5,
“name”: “John Doe”
}
{
“age”: 5,
“name”: “John Doe”,
“firstName”: “John”,
“lastName”: “Doe”
}
{
“age”: 5,
“firstName”: “John”,
“lastName”: “Doe”
}
PROVIDER v1 v2 v3
LATEST QADEV PRODUCTION
v3 v3v3 v2PROVIDER
v2 v1v2 v1CONSUMER A
(age, name)
v1 v1v1 v1CONSUMER B
(age)

28. {
“age”: 5,
“name”: “John Doe”
}
{
“age”: 5,
“name”: “John Doe”,
“firstName”: “John”,
“lastName”: “Doe”
}
{
“age”: 5,
“firstName”: “John”,
“lastName”: “Doe”
}
PROVIDER v1 v2 v3
LATEST QADEV PRODUCTION
v3 v2v3 v2PROVIDER
v2 v1v2 v1CONSUMER A
(age, name)
v1 v1v1 v1CONSUMER B
(age)

29. {
“age”: 5,
“name”: “John Doe”
}
{
“age”: 5,
“name”: “John Doe”,
“firstName”: “John”,
“lastName”: “Doe”
}
{
“age”: 5,
“firstName”: “John”,
“lastName”: “Doe”
}
PROVIDER v1 v2 v3
LATEST QADEV PRODUCTION
v3 v2v3 v2PROVIDER
v2 v2v2 v1CONSUMER A
(age, name)
v1 v1v1 v1CONSUMER B
(age)

30. {
“age”: 5,
“name”: “John Doe”
}
{
“age”: 5,
“name”: “John Doe”,
“firstName”: “John”,
“lastName”: “Doe”
}
{
“age”: 5,
“firstName”: “John”,
“lastName”: “Doe”
}
PROVIDER v1 v2 v3
LATEST QADEV PRODUCTION
v3 v3v3 v3PROVIDER
v2 v2v2 v1CONSUMER A
(age, name)
v1 v1v1 v1CONSUMER B
(age)

31. {
“age”: 5,
“name”: “John Doe”
}
{
“age”: 5,
“name”: “John Doe”,
“firstName”: “John”,
“lastName”: “Doe”
}
{
“age”: 5,
“firstName”: “John”,
“lastName”: “Doe”
}
PROVIDER v1 v2 v3
LATEST QADEV PRODUCTION
v3 v3v3 v3PROVIDER
v2 v2v2 v2CONSUMER A
(age, name)
v1 v1v1 v1CONSUMER B
(age)

32. Want to learn more?

33. Learning Resources
❏ Pact documentation: https://docs.pact.io
❏ Github repos: https://github.com/pact-foundation
❏ Articles:
❏ Consumer-Driven Contracts
❏ De-coupling releases using Pact Broker
❏ Testing Strategies in a Microservices Architecture

34. THANK YOU
For questions or suggestions:
Ama Asare
Danilo Sato