How can I establish conditions on test inputs when performing Property-based testing?

Question

For example, the following code generates bools when I need ints:

Gen.map (fun v -> v > 0)

Here's the function:

[<Property(QuietOnSuccess = true)>]
let ``number of cells in grid equals rowcount squared`` () =
    let values = Arb.generate<int> |> Gen.map (fun v -> v > 0) 
                                   |> Arb.fromGen

I need something like this so that I can get qualifying ints:

Gen.filter (fun v -> v > 0)

However, I just don't see an option for this.

Any suggestions?

Dude, I'm starting to get the hang of FSharp now. I'm still not on your level though. I took a two week break from coding and now I'm back. — Scott Nimrod, May 12 '16 at 14:19
Of interest: [FsCheck - generators, shrinkers and Arbitrary instances](https://fscheck.github.io/FsCheck/TestData.html#Test-data-generators-shrinkers-and-Arbitrary-instances) — Guy Coder, May 12 '16 at 15:11
Of interest: [FsCheck - Gen](https://fscheck.github.io/FsCheck/reference/fscheck-gen.html) — Guy Coder, May 12 '16 at 15:16
Of interest: [Use FsCheck to create random dummy data](https://fsharpforfunandprofit.com/posts/low-risk-ways-to-use-fsharp-at-work-3/#test-dummy) — Guy Coder, May 12 '16 at 16:54
We've now [added `Gen.filter` to FsCheck](https://github.com/fscheck/FsCheck/pull/244). — Mark Seemann, May 13 '16 at 12:54

score 1 · Accepted Answer · edited May 13 '16 at 05:16

1

Try Gen.suchThat (fun v -> v > 0)

edited May 13 '16 at 05:16

Mark Seemann

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answered May 12 '16 at 15:12

Ray

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How can I establish conditions on test inputs when performing Property-based testing?

1 Answers1