My talk from NordicAPIs 2018: https://nordicapis.com/sessions/contract-testing-of-websockets-functional-programming-is-taking-the-stage/

1. Contract Testing of WebSockets:
Functional Programming is taking the Stage
Artem Demchenkov
Illustration © Caterina Carraro/Billie

2. 2
Artem Demchenkov
● CTO & Co-Founder at Billie
● ardemchenkov@gmail.com
● https://www.linkedin.com/in/artem-demchenkov-76b69934/

3. Billie
We are an innovative financial platform, focused on working capital financing.
Some numbers:
● Start: 01.12.2016
● Closed Beta: 01.05.2017
● Public Launch: 01.06.2017
● Team: 36
● Engineering Crew: 18

4. Frontend/Backend communication process at Billie
4
Frontend BackendPush Server
1.WebSocket Connection
5. WebSocket Push 4. API Endpoint Push
3. Change2. WebSocket Authorization

5. Testing at Billie
5
● Unit Testing (PHPUnit)
● Functional Testing (Behat, PHPUnit)
● End-to-End Testing (Selenium, Java)
● API Testing (Postman Collections)
● Contract Testing (Pact.io)
● Load Testing (JMeter, Gatling)
● Penetration Testing (OWASP, External audit)
● Chaos Engineering / Monkey Testing

6. Pact Contract Testing
6
Consumer ProviderMock Server
1. Actual Request
2. Expected Response 4. Actual Response
3. Expected Request

7. 7
Contract Testing
is a perfect way
to test
WebSocket Communication

8. What makes it possible
8
● Backend is a Provider of data
● Frontend is a Consumer of data
● Push Server is a unit, responsible for communication. Same as Mock Server
● FE/BE Pact is a collection of two Interactions
○ WS Connection/Authorization
○ Backend - Frontend Push

9. What else makes it possible. Erlang Worldview *
9
● Everything is a process
● Processes have unique names
● If you know the name of a process you can send it a message
● Processes do what they are supposed to do or fail
* as Joe Armstrong, co-inventor of Erlang, summarized in his PhD thesis

10. Contract Testing of WebSockets
10
Consumer (Process) Test (Process)Push Server (Process)
3. Interaction 1
5. Interaction 2
1. Start
2. Start
4. Verification 1
6. Verification 2

11. 11
Demo

12. What if not «Everything is a process»? E.g. PHP
12
Consumer (Object) Test (Process)Push Server (Process)
3. Interaction 1
5. Interaction 2
1. Start
2. Create
4. Verification 1
6. Verification 2

13. Thank you
● ardemchenkov@gmail.com
● https://www.linkedin.com/in/artem-demchenkov-76b69934/

14. Check it out. There’s interesting
More in our “Engineering Corner” on Medium
14
https://medium.com/billie-finanzratgeber