Testing

Introduction

This document implements a simple org.http4s.HttpRoutes and then walk through the results of applying inputs, i.e. org.http4s.Request, to the service, i.e. org.http4s.HttpService.

After reading this doc, the reader should feel comfortable writing a unit test using his/her favorite Scala testing library.

Now, let’s define an org.http4s.HttpService.

import cats.implicits._
import io.circe._
import io.circe.syntax._
import io.circe.generic.semiauto._
import cats.effect._
import org.http4s._
import org.http4s.circe._
import org.http4s.dsl.io._
import org.http4s.implicits._
case class User(name: String, age: Int)  
implicit val UserEncoder: Encoder[User] = deriveEncoder[User]
// UserEncoder: Encoder[User] = io.circe.generic.encoding.DerivedAsObjectEncoder$$anon$1@339bcdb1

trait UserRepo[F[_]] {
  def find(userId: String): F[Option[User]]
}

def service[F[_]](repo: UserRepo[F])(
      implicit F: Effect[F]
): HttpRoutes[F] = HttpRoutes.of[F] {
  case GET -> Root / "user" / id =>
    repo.find(id).map {
      case Some(user) => Response(status = Status.Ok).withEntity(user.asJson)
      case None       => Response(status = Status.NotFound)
    }
}

For testing, let’s define a check function:

// Return true if match succeeds; otherwise false
def check[A](actual:        IO[Response[IO]], 
            expectedStatus: Status, 
            expectedBody:   Option[A])(
    implicit ev: EntityDecoder[IO, A]
): Boolean =  {
   val actualResp         = actual.unsafeRunSync()
   val statusCheck        = actualResp.status == expectedStatus 
   val bodyCheck          = expectedBody.fold[Boolean](
       actualResp.body.compile.toVector.unsafeRunSync().isEmpty)( // Verify Response's body is empty.
       expected => actualResp.as[A].unsafeRunSync() == expected
   )
   statusCheck && bodyCheck   
}

Let’s define service by passing a UserRepo that returns Ok(user).

val success: UserRepo[IO] = new UserRepo[IO] {
  def find(id: String): IO[Option[User]] = IO.pure(Some(User("johndoe", 42)))
}
// success: UserRepo[IO] = repl.MdocSession$App$$anon$3@64f4181b

val response: IO[Response[IO]] = service[IO](success).orNotFound.run(
  Request(method = Method.GET, uri = uri"/user/not-used" )
)
// response: IO[Response[IO]] = Map(
//   Suspend(org.http4s.HttpRoutes$$$Lambda$11901/778537953@396a325e),
//   cats.data.OptionT$$Lambda$11904/1491900386@14469f79,
//   0
// )

val expectedJson = Json.obj(
  ("name", Json.fromString("johndoe")),
  ("age",  Json.fromBigInt(42))
)
// expectedJson: Json = JObject(object[name -> "johndoe",age -> 42])

check[Json](response, Status.Ok, Some(expectedJson))
// res0: Boolean = true

Next, let’s define a service with a userRepo that returns None to any input.

val foundNone: UserRepo[IO] = new UserRepo[IO] {
  def find(id: String): IO[Option[User]] = IO.pure(None)
} 
// foundNone: UserRepo[IO] = repl.MdocSession$App$$anon$4@79dd3e05 

val response: IO[Response[IO]] = service[IO](foundNone).orNotFound.run(
  Request(method = Method.GET, uri = uri"/user/not-used" )
)
// response: IO[Response[IO]] = Map(
//   Suspend(org.http4s.HttpRoutes$$$Lambda$11901/778537953@3dadd5e5),
//   cats.data.OptionT$$Lambda$11904/1491900386@553df8cc,
//   0
// )

check[Json](response, Status.NotFound, None)
// res1: Boolean = true

Finally, let’s pass a Request which our service does not handle.

val doesNotMatter: UserRepo[IO] = new UserRepo[IO] {
  def find(id: String): IO[Option[User]] = IO.raiseError(new RuntimeException("Should not get called!"))
} 
// doesNotMatter: UserRepo[IO] = repl.MdocSession$App$$anon$5@75200845 

val response: IO[Response[IO]] = service[IO](doesNotMatter).orNotFound.run(
  Request(method = Method.GET, uri = uri"/not-a-matching-path" )
)
// response: IO[Response[IO]] = Map(
//   Suspend(org.http4s.HttpRoutes$$$Lambda$11901/778537953@651d3df2),
//   cats.data.OptionT$$Lambda$11904/1491900386@36ccce49,
//   0
// )

check[String](response, Status.NotFound, Some("Not found"))
// res2: Boolean = true

Conclusion

The above documentation demonstrated how to define an HttpService[F], pass Request’s, and then test the expected Response.

To add unit tests in your chosen Scala Testing Framework, please follow the above examples.

References