CODEWITHSUNDEEP
f#fscheck
Pavel Voronin
Pavel Voronin

Reputation: 13983

How do I prevent shrinking in Model-based testing?

Here's the example of model-based test in FsCheck:

let spec =
  let inc = { new Command<Counter, int>() with
                    override __.RunActual counter = counter.Inc(); counter
                    override __.RunModel m = m + 1
                    override __.Post(counter, m) = counter.Get = m |@ sprintf "model: %i <> %A" m counter
                    override __.ToString() = "inc" }
                           
  let dec = { new Command<Counter, int>() with
                    override __.RunActual counter = counter.Dec(); counter
                    override __.RunModel m = m - 1
                    override __.Post(counter, m) = counter.Get = m |@ sprintf "model: %i <> %A" m counter
                    override __.ToString() = "dec" }
  
  { new ICommandGenerator<Counter,int> with
      member __.InitialActual = Counter()
      member __.InitialModel = 0
      member __.Next model = Gen.elements [inc;dec] }

How do I disable shrinking of commands for this test?

Upvotes: 1

Views: 90

Answers (1)

Brian Berns
Brian Berns

Reputation: 17038

If you want to prevent FsCheck from shrinking the number of commands used (see my question above), you can convert the spec to a property that disables shrinking:

let property =
    let generator = Command.generate spec
    let shrinker _ = Seq.empty   // disable
    Command.toPropertyWith spec generator shrinker
Check.Quick(property)

This allows FsCheck to generate command sequences that are longer than necessary. E.g. [inc; inc; dec; inc; inc; dec; dec; dec].

Upvotes: 1

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