scalacheck: Generate a non empty string

Question

What is the best way to generate a non empty string, when in the context of something like this

  private def createIndexFn() = {
      for{
        someChar <-  Gen.alphaString
        aNumber <- Gen.choose(1,100)
        //...
       }       
       yield { 
           MyThing(AnotherType(someChar.toString), SomeOtherType(aNumber), aNumber)
   }
 }

where you need maybe someChar to be a non empty string. I know you can use whenever in the forAll section but I wonder how to do it in this part of the generator.

Thanks

score 17 · Accepted Answer · answered Jan 30 '18 at 19:36

17

The accepted answer caused a high ratio of discarded tests for me, I ended up using:

import org.scalacheck._

Arbitrary(Gen.nonEmptyListOf[Char](Arbitrary.arbChar.arbitrary)).map(_.mkString))

answered Jan 30 '18 at 19:36

Matthew Pickering

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score 13 · Answer 2 · edited Jan 04 '21 at 14:09

13

What I was looking for was:

import org.scalacheck.Arbitrary.arbitrary

arbitrary[String].suchThat(!_.isEmpty)

and can be used like

for {
  name <- arbitrary[String].suchThat(!_.isEmpty)
  age  <- Gen.choose(0, 100)
} yield Person(name, age)

Hopefully this helps someone

edited Jan 04 '21 at 14:09

Andrii Abramov

10,019
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answered Aug 31 '16 at 11:19

roundcrisis

17,276
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3

It could help more if you add the imports required to make it compiles ;) – Jules Ivanic Aug 06 '17 at 19:12

score 1 · Answer 3 · answered Jul 01 '21 at 11:11

Another way is to create a fix length random string

Gen.listOfN(10, Gen.asciiPrintableChar).map(_.mkString)

or to create a random length with a constrained length

for {
  n     <- Gen.chooseNum(5, 20)
  chars <- Gen.listOfN(n, Gen.asciiPrintableChar)
} yield chars.mkString

scalacheck: Generate a non empty string

3 Answers3