猫 EitherT 和效果的匹配器

Question

我是 cats 和函数式编程的新手，我正在为 EitherT 等函数式数据类型的单元测试而苦苦挣扎。有示例代码：

class Library[F[_]]() {
    def create(book: Book)(implicit M: Monad[F]): EitherT[F, BookAlreadyExistsError, Book] = ...
}

我想使用 Spec2 对其进行测试，但我不知道如何正确进行。试过这样的东西但它不起作用：

  val library = Library[IO]()

  test("create book") {

    val book = Book("Title 1", 2016, "author 1")
    (for (
      resultBook <- library.create(book)
    ) yield resultBook shouldEqual ???
    ).unsafeRunSync()

  }

我想要像这样的非常简单的断言：

   resultBook shouldEqual Right(Book("Title 1", 2016, "author 1"))
   // or
   resultBook shouldEqual Left(BookAlreadyExistsError)

Answer 1

specs2-cats provides IOMatchers 启用以下语法的特性

library.create(book).value must returnValue(Right(book))

哪里

libraryDependencies += "org.specs2" %% "specs2-core" % "4.8.1" % Test,
libraryDependencies += "org.specs2" %% "specs2-cats" % "4.8.1" % Test,

这是一个工作示例

import cats.data.EitherT
import cats.effect.IO
import org.specs2.mutable.Specification
import org.specs2.matcher.IOMatchers

class CatsSpec extends Specification with IOMatchers {
  case class Book(title: String, year: Int, author: String)
  def create(book: Book): EitherT[IO, String, Book] = EitherT(IO(Right(book).withLeft[String]))
  val book = Book("Title 1", 2016, "author 1")

  "specs2-cats dependency" should {
    "provide matcher for IO effect" in {
      create(book).value must returnValue(Right(book))
    }
  }
}