Hey is it possible to generate a random instance based on a class using Arb? something like Arb.next...

# kotest

[André Martins]

Hey is it possible to generate a random instance based on a class using Arb? something like Arb.next<MyType>()?

[Emil Kantis]

Yes. Arb.bind or Arb.data (Alias for bind)

[Emil Kantis]

Arb.bind(
  <http://Arb.int|Arb.int>(),
  Arb.string(codepoints = Codepoint.alphanumeric()),
  ::Student
)

[Emil Kantis]

Another option:

Arb.data<Student>(providedArbs = mapOf(String::class to Codepoint.alphanumeric()))

[Emil Kantis]

a bit tricky when using String for instance, since the provided arbs will work for all values of that type

[André Martins]

Ya true

[Davio]

You can also use DataFaker to have some more realistic names and combine that with your custom generator 🙂

[André Martins]

I just wanted to override a specific field without the need to define every arb for every field with arbitrary block

[Davio]

I guess you could do it like this:

val studentArb = arbitrary {
            val student = Arb.data<Student>().bind()
            student.copy(name = Arb.string(codepoints = Codepoint.alphanumeric()).bind())
        }

[Davio]

But I agree it would be good to have more control over the generation for specific fields

[Davio]

The providerArbs in Arb.data works on types, not field names, so some sort of generator with field names could be useful

[Davio]

In this case the example is small enough that I wouldn't mind a simple arbitrary and just map the fields explicitly

[Emil Kantis]

Reflective binding with overriding per field should be doable I think. Worth investigating

[André Martins]

I totally agree for instance im having issues because the default Arb for OffsetDateTime uses too much memory resulting in out of memory exception in my unit tests 😛

[Davio]

Probably due to the zoneOffsets 🙂

[Emil Kantis]

Created a POC.. definitely seems doable 🙂

[Emil Kantis]

Shit.. I was hoping the cast would filter out properties for irrelevant classes, but seems to pass due to type-erasure 😞

nvm, solved. was possible to reflectively check the type of the property to make sure it matched the class being constructed