Matchers for cats EitherT and effects - scala

Question

I'm new in cats and functional programming and I'm struggling with unit testing functional data types like EitherT. Having example code:
class Library[F[_]]() {
def create(book: Book)(implicit M: Monad[F]): EitherT[F, BookAlreadyExistsError, Book] = ...
}
I'd like to test it using Spec2 but I don't know how to do it properly. Tried something like this but it does not work:
val library = Library[IO]()
test("create book") {
val book = Book("Title 1", 2016, "author 1")
(for (
resultBook <- library.create(book)
) yield resultBook shouldEqual ???
).unsafeRunSync()
}
I'd like to have very simple assertions like this:
resultBook shouldEqual Right(Book("Title 1", 2016, "author 1"))
// or
resultBook shouldEqual Left(BookAlreadyExistsError)

Answer 1

specs2-cats provides IOMatchers trait which enables the following syntax
library.create(book).value must returnValue(Right(book))
where
libraryDependencies += "org.specs2" %% "specs2-core" % "4.8.1" % Test,
libraryDependencies += "org.specs2" %% "specs2-cats" % "4.8.1" % Test,
Here is a working example
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))
}
}
}