Consumer Driven Contracts like TDD to the API by Olga Maciaszek-Sharma & Marcin Grzejszczak at SpringOne Tour 2019

1. 1 © 2019 Pivotal
Consumer Driven Contracts
like TDD to the API
Olga Maciaszek-Sharma, @olga_maciaszek
Marcin Grzejszczak, @mgrzejszczak

2. 2
Spring Cloud developer at Pivotal
Working mostly on
● Spring Cloud Contract
● Spring Cloud Netflix
● Spring Cloud Gateway
About us
Twitter: @olga_maciaszek

3. 3
Spring Cloud developer at Pivotal
Working mostly on
● Spring Cloud Sleuth
● Spring Cloud Contract
● CI / CD
About us
Twitter: @mgrzejszczak
Blog: http://toomuchcoding.com

4. 4
Introduction
Demo
Summary
Agenda

5. 5
What we will NOT be talking about?

6. 6
● Schema
● WSDL
● ESB
● XSD
● XSLT
What we will NOT be talking about?
THE IDEA OF SPRING
CLOUD CONTRACT IS
NOT TO INTRODUCE
UNNECESSARY
COUPLING OR
REPLICATE OLD
MISTAKES

7. 7
● Producer
○ service that exposes an API / sends a message
● Consumer
○ service that consumes the API of the producer / listens to a message
from the producer
● Contract
○ agreement between producer and consumer how the API / message
will look like
● Consumer Driven Contracts
○ approach where the consumer drives the changes of the API of the
producer
Introduction

8. 8
● Stub validity & reusability in the integration tests
● Nice API creation
Introduction
What problems are we trying to solve?

9. 9
Introduction
Typical situation
HTTP
CONSUMER PRODUCER

10. 10
Introduction
How to write a test for it?
HTTP
CONSUMER PRODUCER

11. 11
Introduction
How to write a test for it?
HTTP
CONSUMER PRODUCER

12. 12
WireMock
http://wiremock.org/

13. 13
Introduction
A typical scenario
WE’RE ON THE CONSUMER SIDE!!
CONSUMER OWNS THE STUB
DEFINITIONS

14. 14
Introduction
Stub validity & reusability

15. 15
Introduction
Let’s assume that we’re
introducing a new endpoint...
15

16. 16
Introduction
New endpoint
16

17. 17
● I write the missing code to work with the new URL
● The unit and integration tests pass
● Now we deploy to an environment
where real integrations take place...
Introduction
So now what?

18. 18
Introduction
Ooops...

19. 19
Stubs that were used in the build phase have nothing to do with the real API!!
Introduction
What went wrong?
HTTP
CONSUMER PRODUCER
TEST
OK
HTTP
CONSUMER PRODUCER
REALITY
WAT?!

20. 20
Stubs that were used in the build phase have nothing to do with the real communication!!
Introduction
Another example with messaging
CONSUMERPRODUCER
TEST
PRODUCER CONSUMER
REALITY
topic:
bar
topic:
foo
topic:
bar

21. 21
● Stubs reside with the consumer
● Consumer controls the stubbing process
● How are you sure that the stubs are valid?
● What if other teams want to reuse those stubs?
● How are you sure you’re listening to the proper topic / queue?
● Are you sure you’ll deserialize your message properly?
Introduction
Stub validity & reusability - typical problems

22. 22
● It’s the consumer that uses the API
● Consumers should take part in the creation of the API of the
producer
● The producer’s API change should be driven by consumers
Introduction
Nice API creation

23. 23
Introduction
Nice API creation - no cooperation results

24. 24
Introduction
Nice API creation - no cooperation results

25. 25
Demo
Potential answer
Spring Cloud Contract

26. 26
● Consumer
○ service that gets beer requests
○ has to ask another service if the client can get the beer
● Producer
○ service that checks if the client is old enough to buy beer
● Feature
○ if the user is too young - the beer will not be sold
○ otherwise the beer will be granted
Demo
What are we going to code?

27. 27
Introduction
What are we going to code?
I’m 22 give me a beer
CONSUMER PRODUCER
THERE YOU GO
Can the beer be sold?
status: OK, name: marcin

28. 28
Introduction
What are we going to code?
I’m 17 give me a beer
CONSUMER PRODUCER
GET LOST
Can the beer be sold?
status: NOT_OK, name: marcin

29. 29
Demo
Who is who?
WHITE TERMINAL
WHITE IDE
CONSUMER
BLACK TERMINAL
BLACK IDE
PRODUCER

30. 30
Demo
Consumer’s
offline work
Consumer Phase 1 Consumer Phase 2
Consumer’s
switching to online
Producer phase
Producer’s
implementing
the feature

31. 31
Demo
PRODUCER
CONSUMER
CLONES
PRODUCER
PRODUCER
CLONE
Consumer flow 1
CONSUMER

32. 32
Demo
PRODUCER CONSUMER
CONSUMER
CLONES
PRODUCER
PRODUCER
CLONE
INTERACTION
Consumer flow 1

33. 33
Demo
PRODUCER CONSUMER
PRODUCER
CLONE
INTERACTION
CONSUMER FILES
A PR
Consumer flow 1

34. 34
Demo

35. 35
Demo
PRODUCER
TAKES OVER
THE PR
Producer flow

36. 36
Demo
PRODUCER
TAKES OVER
THE PR
Producer flow
WRITES THE
MISSING
IMPLEMENTATIO
N

37. 37
Demo
PRODUCER
TAKES OVER
THE PR
Producer flow
WRITES THE
MISSING
IMPLEMENTATIO
N
MERGES TO MASTER
CI UPLOADS TO NEXUS /
ARTIFACTORY

38. 38
Demo

39. 39
Demo
CONSUMER
Consumer flow 2
SWITCHES
TO ONLINE
MODE
DOWNLOADS STUBS
OF COLLABORATORS
DURING BUILD PHASE

40. 40
Demo

41. 41
I don’t want to write any scripts!

42. 42
Spring Cloud Contract with YML
Don’t worry! You can use
Spring Cloud Contract with YML
42

43. 43
Spring Cloud Contract with YML
43

44. 44
Spring Cloud Contract with Swagger
If you must… then you can also use
Swagger definitions
44

45. 45
Spring Cloud Contract with Rest Docs
You can also use
Spring Cloud Contract with Rest Docs!!
45

46. 46
With Spring Cloud Contract and Consumer Driven Contracts:
● we’ve created an API that suits the consumer and the producer
● expectations were defined by readable contracts
● expectations were tested against the producer
● producer stubs can be reused by consumers
● starting and setting stubs is fully automated
Summary

47. 47
Learn More. Stay Connected.
▪ Read the docs
http://cloud.spring.io/spring-cloud-contract/
▪ Check the samples
https://github.com/spring-cloud-samples/spring-cloud
-contract-samples
▪ Talk to us on Gitter
https://gitter.im/spring-cloud/spring-cloud-contract
Twitter: twitter.com/springcentral
YouTube: spring.io/video
LinkedIn: spring.io/linkedin
Google Plus: spring.io/gplus

48. 48
QUESTIONS