I've done a fair bit of testing with ScalaCheck. I do think it's useful to define your "generators" for your domain model(s), because without them, unit tests can end up being mostly data creation code. With your generators out in their own (testing) package, and named appropriately, you can get quite a bit of mileage out of them, even if you don't take advantage of the property-based testing framework beyond that. Something like..

    object Generators {

      val commentsGen: Gen[Comment] = ???
      val userWithTwoCommentsGen: Gen[User] = Gen.listOfN(2)(commentsGen).map(comments => new User(comments))

      val userWithNoCommentsGen: Gen[User] = Gen.const(new User(List.empty)
    
      val userGen: Gen[User] = Gen.listOf(comments).map(comments => new User(comments))
    }

And then your test code can get right to the point so to speak

    "Users with comments" should "karma equal to the sum of their posts" in {
      val users = Generators.userGen.take(10).foreach(u =>
        u.karma should be (u.comments.map(_.points).sum)
      )
    }