How to generate random unicode strings?

Question

For testing purposes, you may want to supply random input to a method, but Alphanumeric generators like scala.util.Random.alphanumeric don't cover the full possible input in many cases.

What is the best way to generate random unicode strings of a given length?

Answer 1

Consider ScalaCheck generators, for example

import org.scalatest._
import org.scalatestplus.scalacheck.ScalaCheckDrivenPropertyChecks
import org.scalacheck.{Arbitrary, Gen}

class AlphanumericGeneratorSpec extends FlatSpec with Matchers with ScalaCheckDrivenPropertyChecks {
  "Arbitrary.arbString" should "generate arbitrary strings" in {
    forAll(Arbitrary.arbString.arbitrary) { s =>
      println(s)
    }
  }
}

outputs something like

⦍鸟㗴鲪ᬎ㺥
䊪仍ୁ㕃댊벝蛎瓊倊錾釨㚺㥌ੜ
仁벵ຝ洱霷쀙쵟㹳灢瑤쌴
詢蓫䑽ᵋ앹䦆딂෡ᄬ鉖
醃䦼컠᳞遱掊醌涰ᚕ苇泟Ễ㒪뭩綗ᄍ䉱屮藓䦆䜜㴹煉ں㸲䛊ᓠ셴켶䦖垯ᡤ卆婱羘畕⁋䢅ﯫ訆݊ⵕ건
썁㙁䠼臩蚁䬣ݍ⓸⤵犕꺭ཛྷ잁闓襥鯽啌ꟴ翏㫺ܪሷ뢛快腊机ᰵ蟽ﳥɴ೑馣䪚軇鿾㹄Ꝓ㿈뿭땧颟ᜒ纈ꔧ毚뒢兊屼
矵귳옘䕌Ⱌ｀凣쐕튌ằ惿獄ꍝ䫗끒뮌錑꓌㶩ዒ絽໸鹣煋襁ꨔᔵ팋屜姙ꙇᡛ뾗꘎焑酸ಹ乵텣쳊疟䉴﬈투꿠㱎ᅧ텎ᑽﹽ跡
橛櫯ꆠ葲逊ᵈ엦災盨捻棉䟔縆⦽㯠侄ᙑד볓끀謹翆滳ץ픎Ꝛ餮范샥➮⊠㇔鐿詥ꊔ텦䟑徜ꮉ绳䜁빎학⮴䑢悋铃揍挛⭂장踛ﻥ螴阶ퟠ햇
ᶭ䯵꧓擃轤ꦧꦛ

To set fixed size try

def arbUnicodeGen(size: Int) = 
  Gen.listOfN(size, Arbitrary.arbChar.arbitrary).map(_.mkString)

and then

  "arbUnicodeGen" should "generate fixed length arbitrary strings" in {
    forAll(arbUnicodeGen(10)) { s =>
      println(s)
    }
  }

Answer 2

It can be done without mutable buffers or variables.

import java.lang.Character
import util.Random

def randomUnicodeString(length: Int) =
  LazyList.continually(Random.nextInt(0xFFFF))
          .collect{case c if Character.isDefined(c) => c.toChar}
          .take(length)
          .mkString