embracing-nondeterminism-code/src/test/scala/green/thisfieldwas/embracingnondeterminism/data/ListSpec.scala

package green.thisfieldwas.embracingnondeterminism.data

import green.thisfieldwas.embracingnondeterminism.util._
import org.scalacheck.Gen
import org.scalatest.Inside
import org.scalatest.matchers.should.Matchers
import org.scalatest.wordspec.AnyWordSpec

class ListSpec extends AnyWordSpec with Matchers with Inside {

  "List" can {
    "head" which {
      "faults" when {
        "the list is empty" in {
          inside(the[NoSuchElementException].thrownBy(Nil.head)) { case e: NoSuchElementException =>
            e.getMessage shouldBe "Nil.head"
          }
        }
      }
      "gets the first element" when {
        "the list is not empty" in {
          List(1, 2, 3).head shouldBe 1
        }
      }
    }

    "tail" which {
      "faults" when {
        "list list is empty" in {
          inside(the[NoSuchElementException].thrownBy(Nil.tail)) { case e: NoSuchElementException =>
            e.getMessage shouldBe "Nil.tail"
          }
        }
      }
      "gets all but the first element" when {
        "the list is not empty" in {
          List(1, 2, 3).tail shouldBe List(2, 3)
        }
      }
    }

    "isEmpty" which {
      "is true" when {
        "the list is empty" in {
          List[Int]().isEmpty shouldBe true
        }
      }
      "is false" when {
        "the list is not empty" in {
          List(1, 2, 3).isEmpty shouldBe false
        }
      }
    }

    "foldLeft" which {
      "returns the accumulator" when {
        "the list is empty" in {
          List[Int]().foldLeft(0)(_ + _) shouldBe 0
        }
      }

      "applies the function" when {
        "the list is non-empty" in {
          List(1, 2, 3).foldLeft("$")(_ + _.toString) shouldBe "$123"
        }
      }
    }

    "foldRight" which {
      "returns the accumulator" when {
        "the list is empty" in {
          List[Int]().foldRight(0)(_ + _) shouldBe 0
        }
      }

      "applies the function" when {
        "the list is non-empty" in {
          List(1, 2, 3).foldRight("$")(_.toString + _) shouldBe "123$"
        }
      }
    }

    "reverse" which {
      "reverses the order of instances in the list" in {
        List(1, 2, 3, 4, 5).reverse shouldBe List(5, 4, 3, 2, 1)
      }
    }

    "zip" which {
      "zips two lists of equal length together" in {
        List(1, 2, 3, 4).zip(List("a", "b", "c", "d")) shouldBe List((1, "a"), (2, "b"), (3, "c"), (4, "d"))
      }
      "zips two lists with the left list being shorter" in {
        List(1, 2, 3).zip(List("a", "b", "c", "d")) shouldBe List((1, "a"), (2, "b"), (3, "c"))
      }
      "zips two lists with the right list being shorter" in {
        List(1, 2, 3, 4).zip(List("a", "b", "c")) shouldBe List((1, "a"), (2, "b"), (3, "c"))
      }
    }

    "::" which {
      "prepends an element to the list" in {
        0 :: List(1, 2, 3) shouldBe List(0, 1, 2, 3)
        0 :: Nil shouldBe List(0)
      }
    }

    "|:" which {
      "creates a NonEmptyList" in {
        0 |: List(1, 2, 3) shouldBe NonEmptyList(0, List(1, 2, 3))
        0 |: Nil shouldBe NonEmptyList(0)
      }
    }

    "toSeq" which {
      "converts the List to a Seq" in {
        List(1, 2, 3).toSeq shouldBe Seq(1, 2, 3)
      }
    }
  }

  "List object" can {
    "apply" which {
      "creates an empty list" when {
        "given no arguments" in {
          List[Int]() shouldBe Nil
        }
      }
      "creates a list with elements" when {
        "given arguments" in {
          List(1, 2, 3) shouldBe (1 :: 2 :: 3 :: Nil)
        }
      }
    }

    "unapply" which {
      "matches the length of a list" when {
        "the list has no elements" in {
          List[Int]() match {
            case List() => succeed
            case _      => fail("List should be empty")
          }
        }
        "the list has one element" in {
          List(1) match {
            case List(x) => x shouldBe 1
            case _       => fail("List should have one element")
          }
        }
      }
    }
  }

}

/** Check that `List` conforms to typeclass laws.
  */
class ListLaws extends Laws with FunctorLaws {

  /** From a generator for some type `A`, generate a `List` of some length of
    * `A`.
    */
  implicit val listLiftedGen: LiftedGen[List] = new LiftedGen[List] {

    override def lift[A](gen: Gen[A]): Gen[List[A]] =
      Gen.sized(Gen.listOfN(_, gen).map(List(_: _*)))
  }

  checkFunctorLaws[List]()
}