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Improving design and
code quality
with Property-based testing
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Strategic Technology Consultants -
Agile Technical Coaches -
Domain-Driven Design - Continuous
Delivery - EventStorming - Example
Mapping
@kenny_baas
baasie.com
@joaoasrosa
joaorosa.io
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@kenny_baas @joaoasrosa
@kenny_baas @joaoasrosa
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@kenny_baas @joaoasrosa
The greatest obstacle to discovery is not ignorance -
it is the illusion of knowledge.
- Daniel J. Boorstin
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@kenny_baas @joaoasrosa
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@kenny_baas @joaoasrosa
Testing should be about:
Learning from mistakes
instead of only confirming
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@kenny_baas @joaoasrosa
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@kenny_baas @joaoasrosa
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@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
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@kenny_baas @joaoasrosa
Testing should be about:
Living documentation on
behaviour instead of on data
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@kenny_baas @joaoasrosa
Dave Farley - Continuous Delivery
Feedback
Quickly
Timely
Reliable
Customer
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@kenny_baas @joaoasrosa
Releasing software is too often an art;
it should be an engineering discipline
- Dave Farley
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@kenny_baas @joaoasrosa
Testing should be about:
Fast feedback on new demands
instead of slow changes
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@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
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@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
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@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
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@kenny_baas @joaoasrosa
Frameworks:
Java Junit4: JUnit-Quickcheck
Java JUnit5: jqwik
C#: FsCheck
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@kenny_baas @joaoasrosa
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@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
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@kenny_baas @joaoasrosa
Software Development is
a learning process, working code is a
side effect
- Alberto Brandolini
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@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
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@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?
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@kenny_baas @joaoasrosa
C#
https://github.com/joaoasrosa/techorama-nl-property-based-testing
Java
https://gitlab.com/Baasie/Property-Based-Testing
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#CatTax