Property-based testing focuses on testing software behavior rather than specific data points by generating random valid and invalid inputs to uncover bugs. It provides quick, timely, and reliable feedback during development. The approach improves code quality by discovering errors early in development through continuous testing and feedback rather than traditional confirmation bias testing.

1. Improving design and
code quality
with Property-based testing

2. Software Consultant - EventStormer
Domain Driven Design
Behaviour Driven Development
Test Driven Development
Continuous Delivery
@kenny_baas
baasie.com
@joaoasrosa
joaorosa.io

12. The greatest obstacle to discovery is not ignorance -
it is the illusion of knowledge.
- Daniel J. Boorstin

14. Confirmation Bias

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18. To communicate effectively, the code must be based on the
same language used to write the requirements
- the same language that the developers speak
with each other and with domain experts
- Eric Evans

20. Dave Farley - Continuous Delivery
Feedback
Quickly
Timely
Reliable
Customer

21. Releasing software is too often an art;
it should be an engineering discipline
- Dave Farley

23. Single abstraction examples (aka Unit tests)
● Learning from mistakes
instead of only confirming
● Fast feedback on new demands
instead of slow changes
● Living documentation on
behaviour instead of on data

28. Human CI
● Always run tests locally before commiting
● Once the code is committed, wait for the result of commited build
○ Don’t go home, to lunch, to a meeting, to make coffee
● If a teammate has gone home, lunch…. revert their changes!
● Fix or revert within 10 minutes
● When there are failures, Pair or Mob and learn together
Dave Farley - Continuous Delivery

29. Software Development is
a learning process, working code is a
side effect
- Alberto Brandolini

30. Benefits
● Covers (eventually) the scope of all data points,
forget about data
● Shrinker looks for a small use case
● Reproducible tests
Next thing -> Fuzzing invalid inputs in System Tests

31. Summary
● (Also) Write tests with the
intention of breaking code
● Forget about data, focus on behaviour!
● Quickly, Timely, Reliable Feedback
● Human CI
● Ohh… Have we mentioned
Domain Driven Design?

32. C#
https://github.com/joaoasrosa/techorama-nl-property-based-testing
Java
https://gitlab.com/Baasie/Property-Based-Testing

33. #CatTax