Improving design and code quality with Property-based testing @ Q-con ABN AMRO 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, 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 Consultant Domain-Driven Design - Continuous Delivery - EventStorming @joaoasrosa joaorosa.io
5. 5 @joaoasrosa
8. 8 @joaoasrosa
10. 10 @joaoasrosa
11. 11 The greatest obstacle to discovery is not ignorance - it is the illusion of knowledge. - Daniel J. Boorstin @joaoasrosa
13. 13 @joaoasrosa
14. 14 @joaoasrosa
15. 15 @joaoasrosa
16. 16 Testing should be about: Learning from mistakes instead of only confirming @joaoasrosa
17. 17 @joaoasrosa
18. 18 @joaoasrosa
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20. 20 @joaoasrosa
21. 21 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 @joaoasrosa
22. 22 Testing should be about: Living documentation on behaviour instead of on data @joaoasrosa
24. 24 Dave Farley - Continuous Delivery Feedback Quickly Timely Reliable Customer @joaoasrosa
25. 25 Releasing software is too often an art; it should be an engineering discipline - Dave Farley @joaoasrosa
26. 26 Testing should be about: Fast feedback on new demands instead of slow changes @joaoasrosa
27. 27 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 @joaoasrosa
28. 28 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 @joaoasrosa
29. 29 Fuzzing in Property-based testing Randomly generate data points within the boundary of a business invariant to verify the behaviour of the system @joaoasrosa
30. 30 Frameworks: Haskell: Quickcheck Java Junit4: JUnit-Quickcheck Java JUnit5: jqwik C# & F#: FsCheck and Hedgehog @joaoasrosa
32. 32 @joaoasrosa
35. 35 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 @joaoasrosa
36. 36 Software Development is a learning process, working code is a side effect - Alberto Brandolini @joaoasrosa
37. 37 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 @joaoasrosa
38. 38 Summary • (Also) Write tests with the intention of breaking code • Forget about data, focus on behaviour! • Quickly, Timely, Reliable Feedback • Human CI • Ohh… Have I mentioned Domain-Driven Design? @joaoasrosa
39. 39 @joaoasrosa C# https://github.com/joaoasrosa/techorama-nl-property-based-testing Java https://gitlab.com/Baasie/Property-Based-Testing