Functional Testing is a very powerful tool in general. It allows performing validation tests for HTTP responses, locating of broken connections and even generating of a number of concurrent requests. And if testing of the stateless HTTP request/response protocol is not a rocket science, testing of WebSockets could be problematic, because messages need to be tested on both sides: client and server. In my talk, I would like to share an experience of how we do it in my current team using Contract Testing pattern and Erlang OTP. Life demo is included, of course.

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
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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
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● 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 *
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● 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

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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