Are there any tools which generate Arbs from class...

# kotest

[nacyolsa]

Are there any tools which generate Arbs from classes? Maybe there were some ideas to create such generator?

[Kev]

Arbs or Args? https://plugins.jetbrains.com/plugin/10942-kotlin-fill-class

[nacyolsa]

Kotest Arbs

[LeoColman]

https://kotest.io/docs/proptest/reflective-arbs.html

[LeoColman]

Maybe this is close to what you're thinking?

[LeoColman]

If you are thinking of "More general arbs" then maybe this https://kotest.io/docs/proptest/property-test-extra-arbs.html is what you were thinking

[nacyolsa]

Sometimes I would need to manually adjust generated Arb

[nacyolsa]

My use case is that I create data class and every time I need to write manually Arb for it

[LeoColman]

Are you doing it through using bind?

[nacyolsa]

yes

[LeoColman]

Then I think there is no such tool.

You'd like to select your data class and say "Generate me the scaffold for a custom Arb that I can modify"

[LeoColman]

Or something like that?

[nacyolsa]

exactly something like that

[LeoColman]

Then I don't think we have it.
It would be a good idea for https://github.com/kotest/kotest-intellij-plugin !

[Emil Kantis]

You can manipulate the arb used for one of the parameters or types. Is that not sufficient?

[Emil Kantis]

I see that we haven’t yet released support to so it by parameter. Slated for 5.9. https://kotest.io/docs/next/proptest/reflective-arbs.html

[Adam S]

I had an idea a while ago to generate arbs from @Serializable classes https://kotlinlang.slack.com/archives/CT0G9SD7Z/p1647451898560189

[nacyolsa]

Reflective Arbs looks great but I'm almost not use ``checkAll`/`forAll`` in my tests. Instead I have Arbs for every class and use them in every test. Very often I need to use custom Arbs instead of using defaults, instead of Arb.string() I need to use `Arb.alphanumeric()`or positiveInt()/int() with Reflective Arbs I would have problem with this in many places because they won't know what exactly kind of Arb is needed.

[sam]

I like the idea of the plugin being able to generate an arb for you, so you can then tweak it manually after.

[Skel]

@nacyolsa
Perhaps the library I maintain would be helped. It is called Fixture Monkey. It is also the third party extension of kotest.
It provides KotestPlugin for generating a custom Arb.
It can generate an Arb instance like Reflective Arbs does, customizing the property with Arb or any other type.

It is the example below.

class StringObject(val string: String)

val arb = FixtureMonkey.builder()  
    .plugin(KotestPlugin())  
    .plugin(KotlinPlugin())  
    .build()
    .giveMeArb<StringObject> { setArb(StringObject::string, Arb.zipcodes()) }

[nacyolsa]

Thanks @Skel, I will check it.

[sam]

@Skel that is a really nice project

[LeoColman]

it's already listed on third-party extensions. Cool

[nacyolsa]

@Skel I started using your cool project and I have one question.
Let's say I have the following class

data class A(val id: Int, val assignments: List<Int>)

How can I configure FixtureMonkey to put id into assignments ? I mean FixtureMonkey generates id and puts it into ``assignments`` without generating it again with random number.

[Skel]

@nacyolsa Sorry for the late reply. I checked Slack now.
In that case, You can use thenApply API.

FixtureMonkey.builder()
    .plugin(KotlinPlugin())
    .build()
    .giveMeBuilder<A>()
.minSizeExp(A::assignments, 1)
.thenApply { a, builder ->
    builder.setExp(A::assignments[0], a.id)
}
.sample()

If you do not want to use this API again, then check out register option in FixtureMonkeyBuilder.
If you have additional questions, please ask on the GitHub issue!