Hey :slightly_smiling_face: I’m currently fiddling around with `property-based-testing` in Kotest. I...

# kotest

[Mervyn McCreight]

Hey 🙂
I’m currently fiddling around with property-based-testing in Kotest. I want to create a custom arbitrary based on already defined arbitraries . I found this page in the documentation about it:
https://kotest.io/docs/proptest/custom-generators.html#arbitrary

In the documentation there is a code snippet about doing it:

val personArb = arbitrary { rs ->
   val names = Arb.string().values(rs)
   val ages = <http://Arb.int|Arb.int>().values(rs)
   names.zip(ages).map { (name, age) -> Person(name.value, age.value) }
}

The concept is clear, but the function values(RandomSource) is deprecated. What am I supposed to use as an alternative in this case? Would it be generate(RandomSource)? The replacement description is not really applicable for this particular case I think. Using samples(RandomSource) seems wrong, because I think it makes sense to keep the edge-cases of the arbs here 🤔 .

[sam]

Docs are prob out of date.

[sam]

let me check

[sam]

https://kotest.io/docs/proptest/custom-generators.html

[sam]

updated to reflect the current state

[Mervyn McCreight]

Cool thanks 🙂

[Mervyn McCreight]

If I have e.g. a data class just containing .. lets say an Int and I need an arb creating instances of that data class.

Would it be fine to just use map on the given Arb?
E.g.:

<http://Arb.int|Arb.int>().map { MyDataClass(it) }

to define an Arb for MyDataClass ?

[sam]

absolutely

[sam]

or Arb.bind(<http://Arb.int|Arb.int>()) { MyDataClass(it) }

[sam]

map is great for single values

[sam]

bind is good for > 1

[sam]

Arb.bind(<http://Arb.int|Arb.int>(), Arb.string()) { a,b -> MyDataClass(a,b) }

[Mervyn McCreight]

ok cool. Thanks for your help 🙂 👍