Lunch & Learn - Property Based Testing

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Lunch & Learn Property based Testing

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What is a Property? Something always true in a given context

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Could be Strong The total is the sum of the elements The answer is always 42 …

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But most of the time, it’s weak The appointment is always in the future The invoice is never negative …

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A test only validate one specific case

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Wait, we also have parameterized tests

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Yes but we go further with random generators

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Let me introduce FsCheck A port of Haskell’s Quickcheck for .NET

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Generator: easily generates a number of random values for many types Shrinker: tries to find the mininal counter example that still fails the property

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Property based testing don’t replace unit testing

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Property based testing test a lot of random cases cheaply

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Random??? So what does green mean? Testing show the presence, not the absence of bug E. W. Dijktra

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Finding good properties is hard

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But it is worth to think about general properties of your business

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Thanks QuickCheck: A Lightweight Tool for Random Testing of Haskell Programs http://www.cs.tufts.edu/~nr/cs257/archive/john-hughes/quick.pdf An introduction to property-based testing http://fsharpforfunandprofit.com/posts/property-based-testing/ FsCheck https://fscheck.github.io/FsCheck/