Property Based Testing for Better Code @jessitron lots of tests - - PowerPoint PPT Presentation

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Property Based Testing for Better Code @jessitron lots of tests - - PowerPoint PPT Presentation

Jun 24, 2023 111 likes •530 views

Property Based Testing for Better Code @jessitron lots of tests maintenance burden didn't test seams Scala ScalaCheck Property Based Testing Scala ScalaCheck Property Based Testing Define Success Design Documentation Quality Enable

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@jessitron

Property Based Testing for Better Code

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lots of tests maintenance burden didn't test seams

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Scala ScalaCheck Property Based Testing

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Scala ScalaCheck Property Based Testing

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Define Success

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Design Documentation Quality Enable Change

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Generators Properties

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Generators

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Generators

Document: what is valid input data? Design: build up from components Quality: automatic corner cases Enable: tests of larger components

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Enable: tests of larger components

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Game Rules # turns Player Player Strategy Strategy

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Rules

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case class Rules(temptationToDefect: Points, rewardForMutualCooperation: Points, punishmentForMutualDefection: Points, suckersPenalty: Points)

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property("The game is fair") = forAll {(rules: Rules, moves: MoveSet) => val oneWay = Rules.score(rules, moves) val theOtherWay = Rules.score(rules, moves.swap)

  • neWay.swap == theOtherWay

}

  • bject RuleTest extends Properties("Prisoners Dilemma") {

}

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property("Defection is always better for me") = forAll {(rules: Rules, theirMove: Move) => val ifIDefect = Rules.score(rules, (Defect, theirMove))._1 val ifICooperate = Rules.score(rules, (Cooperate, theirMove))._1

  • ifIDefect > ifICooperate

}

  • bject RuleTest extends Properties("Prisoners Dilemma") {

}

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A => B

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Properties

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Properties

Document: what is important? Quality: they are always true

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property("The sucker always cooperates") = forAll(strategyGen, Gen.posNum[Int]) { (opponent: Strategy, turns: Int) => val allMoves:Stream[MoveSet] = Strategy.moves(Strategy.sucker, opponent).take(turns) val myMoves = allMoves.map (_._1)

  • myMoves.forall(_ == Cooperate)

}

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Complete properties Incomplete properties Relational properties

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forAll { (list: List[Int] => list.reverse.reverse = list }

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forAll { (input: Input) =>

  • ldWay(input) =? newWay(input)

}

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forAll { (output: Output) => val input = from(output) subject(input) ?= output }

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property("All games end within the time limit") = forAll { (rules: Rules, players: Seq[Player], limit: Duration) => classify(players.size < 10, "small", "large") { val timer = new Timer() val output = Game.eachOnEach(rules)(sys, players, limit) val timeTaken = timer.check val timeOver = timeTaken - limit

  • classify (timeOver < (fudge/2), "comfortable", "barely") {

(timeTaken <= (limit + fudge)) :| s"$timeTaken was longer than $limit" }}}

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Properties

Document: what is important? Design: what do we need to know? Quality: they are always true Enable: changes to less important bits

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What does it make free? What does it make explicit? What does it make impossible?

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Scala ScalaCheck Property Based Testing

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http://www.artima.com/shop/scalacheck

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@jessitron

https://github.com/jessitron/scalacheck-prisoners-dilemma