Improving design and code quality with Property-based testing @ Codemotion Rome 2019

A suite of traditional unit tests will only be as strong as the possible arguments or parameters tested against your code. Quoting Romeu Moura: If you take a String as an argument, then the works of Shakespeare in Japanese & Korean are ONE valid input. Obviously, this can be achieved with parameterized testing. However, this makes the unit tests so big that it is harder to understand which behaviour it is validating. We want our unit tests to also serve as living documentation so they should be comprehensible and to the point.

Enter property-based testing. In property-based testing, we randomly generate data points within the boundary of a property to verify the property’s behaviour. This not only lets us test edge cases that could expose unwanted and unexpected errors in the code but also enables us to make small tests that are readable and clear. Making these tests will also force you to think harder about the problem at hand and improve your design and code quality.

In this technical session, Kenny & João demonstrates and explains what property-based testing is, and how to implement it in C# with FsCheck and Java with JUnit-Quickcheck. If you are interested in improving your unit testing, so you don’t have to worry much about test data anymore, but more about the problem your code is solving, this talk is for you!

Transcript

1. Improving design and code quality with Property-based testing
2. 2 Strategic Technology Consultants - Agile Technical Coaches - Domain-Driven Design - Continuous Delivery - EventStorming - Example Mapping @kenny_baas baasie.com @joaoasrosa joaorosa.io
5. 5 @kenny_baas @joaoasrosa @kenny_baas @joaoasrosa
8. 8 @kenny_baas @joaoasrosa
10. 10 @kenny_baas @joaoasrosa
11. 11 @kenny_baas @joaoasrosa The greatest obstacle to discovery is not ignorance - it is the illusion of knowledge. - Daniel J. Boorstin
13. 13 @kenny_baas @joaoasrosa
14. 14 @kenny_baas @joaoasrosa
15. 15 @kenny_baas @joaoasrosa
16. 16 @kenny_baas @joaoasrosa Testing should be about: Learning from mistakes instead of only confirming
17. 17 @kenny_baas @joaoasrosa
18. 18 @kenny_baas @joaoasrosa
19. blue yellow yellow red green purple blue blue green purple yellow red green yellow purple blue red yellow green red blue purple yellow purple red blue purple blue green yellow red red purple green yellow blue blue yellow green red purple yellow blue green red purple yellow red blue green purple green red yellow purple blue purple green red blue yellow yellow red green purple blue blue green purple yellow red green yellow purple blue red yellow green red blue purple yellow purple red blue green red purple yellow blue green red purple yellow red blue green purple green red yellow purple blue purple green red blue yellow yellow red green purple blue blue green purple yellow red green yellow purple blue red yellow green red blue purple yellow purple red blue green red purple yellow blue green red purple yellow red blue green purple green red yellow purple blue purple green red blue yellow yellow
20. 20 @kenny_baas @joaoasrosa
21. 21 @kenny_baas @joaoasrosa 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
22. 22 @kenny_baas @joaoasrosa Testing should be about: Living documentation on behaviour instead of on data
24. 24 @kenny_baas @joaoasrosa Dave Farley - Continuous Delivery Feedback Quickly Timely Reliable Customer
25. 25 @kenny_baas @joaoasrosa Releasing software is too often an art; it should be an engineering discipline - Dave Farley
26. 26 @kenny_baas @joaoasrosa Testing should be about: Fast feedback on new demands instead of slow changes
27. 27 @kenny_baas @joaoasrosa 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. 28 @kenny_baas @joaoasrosa In comes Property-based testing The construction of tests such that, when these tests are fuzzed, failures in the test reveal problems with the system under test
29. 29 @kenny_baas @joaoasrosa Fuzzing in Property-based testing Randomly generate data points within the boundary of a business invariant to verify the behaviour of the system
30. 30 @kenny_baas @joaoasrosa Frameworks: Java Junit4: JUnit-Quickcheck Java JUnit5: jqwik C#: FsCheck
32. 32 @kenny_baas @joaoasrosa
35. 35 @kenny_baas @joaoasrosa 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
36. 36 @kenny_baas @joaoasrosa Software Development is a learning process, working code is a side effect - Alberto Brandolini
37. 37 @kenny_baas @joaoasrosa 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
38. 38 @kenny_baas @joaoasrosa 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?
39. 39 @kenny_baas @joaoasrosa C# https://github.com/joaoasrosa/techorama-nl-property-based-testing Java https://gitlab.com/Baasie/Property-Based-Testing
40. #CatTax