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  1. Software craftsmanship
  2. Katas
  3. Improve your software quality with Property-Based Testing

A journey to Property-Based Testing

PreviousImprove your software quality with Property-Based TestingNextClean Code

Last updated 3 years ago

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The purpose of this workshop is to understand by the practice an approach to testing that allows us to identify and check our business invariants. We will discover :

  • How it differs from traditional sampling approach (example-based testing)

  • Its advantages and limits

Source code

Source code is available in :

  • Scala : Scalatest / Scalacheck

  • C# 10 : XUnit / FsCheck / Language-Ext / FluentAssertions

Connection - Calculator

Connect participants to the topic by making them write Unit Tests on the Calculator class :

Debriefing :

Concepts - PBT

  • Go through slides 4 to 15 to explain the different concepts :

    • Example-Based Testing vs PBT

    • What is PBT ?

    • Addition properties example

    • PBT by hands

    • Scalacheck / FsCheck / QuickCheck

    • Associated concepts

Concrete Practice

Postal Parcel

Open `PostalParcel` :

  • Identify properties – 5’

  • What are the invariants ?

  • Write them in `PostalParcelPropertiesFlatSpec` with ScalaCheck / FsCheck - 15’

  • Collective debriefing – 5’

Bank withdrawal

  • Open `AccountService` :•Identify properties – 5’

  • What should we do to check those properties ?

  • Demonstrate how you could write properties on those knowing that Command and Account are tightly coupled as inputs :

    • Using properties + input filtering (when)

    • Using properties and Builder

    • How we would write tests on Bank withdrawal in real life (with Parameterized tests

Rental Calculator - PBT as a refactoring tool

  • Open `RentalCalculator`

  • Imagine this code is running in production and business is happy with it

  • Imagine you need to adapt it, but you need to be sure that you don’t introduce any regression

  • How PBT can help us ?

  • Let them code - 15'

  • Collective debriefing - 5'

Conclusion

  • When to apply PBT in real life

  • Associated anti-patterns

  • Reflect : Think about your last development, how this approach could have helped you ?

Resources

Demonstrate how to write properties on the Calculator, you can use the to prepare yourself

Scala exercises on PBT :

Property based testing - step by step :

step-by-step guide
Scala
C#
Scala
C#
ScalaCheck documentation
https://www.scala-exercises.org/scalacheck/generators
"Functions for nothing, and your tests for free" Property-based testing and F# - George Pollard
https://www.leadingagile.com/2018/04/step-by-step-toward-property-based-testing/
here
Slide deck to support workshop