Sharing resources

Resources can be shared across tests, this is done by implementing a method that returns cats.effect.Resource.

This is also how you would translate the traditional beforeAll and afterAll methods, as the resources are acquired before tests are run, and cleaned-up after they finish.

import weaver._
import cats.effect._

// Using http4s
import org.http4s.client.blaze._
import org.http4s.client._
import scala.concurrent.ExecutionContext.global

object HttpSuite extends IOSuite {

  // Sharing a single http client across all tests
  override type Res = Client[IO]
  override def sharedResource : Resource[IO, Res] =
    BlazeClientBuilder[IO](global).resource

  // The test receives the shared client as an argument
  test("Good requests lead to good results") { httpClient =>
    for {
      statusCode <- httpClient.get("https://httpbin.org/get"){
        response => IO.pure(response.status.code)
      }
    } yield expect(statusCode == 200)
  }

  test("Bad requests lead to bad results") { httpClient =>
    for {
      statusCode <- httpClient.get("https://httpbin.org/oops"){
        response => IO.pure(response.status.code)
      }
    } yield expect(statusCode == 404)
  }


}

Resources lifecycle

We can demonstrate the resource lifecycle with this example:

import java.util.concurrent.ConcurrentLinkedQueue

// We will store the messages in this queue
val order = new ConcurrentLinkedQueue[String]()
// order: ConcurrentLinkedQueue[String] = [Acquiring resource, Test 1 is using resource 42, Test 2 is using resource 42, Releasing resource 42]

object ResourceDemo extends IOSuite {

  def record(msg: String) = IO(order.add(msg)).void

  override type Res = Int
  override def sharedResource = {
    val acquire = record("Acquiring resource") *> IO.pure(42)
    val release = (i: Int) => record(s"Releasing resource $i")
    Resource.make(acquire)(release)
  }

  test("Test 1") { res =>
    record(s"Test 1 is using resource $res").as(success)
  }

  test("Test 2") { res => 
    record(s"Test 2 is using resource $res").as(expect(res == 45))
  }
}

repl.MdocSessionMdocAppResourceDemo
+ Test 1 0ms
- Test 2 1ms
*************FAILURES*************
repl.MdocSessionMdocAppResourceDemo
- Test 2 1ms
  assertion failed (resources.md:76)

  record(s"Test 2 is using resource $res").as(expect(res == 45))
                                                     |   |
                                                     42  false
Total 2, Failed 1, Passed 1, Ignored 0, Cancelled 0

Contents of order are:

// * Acquiring resource
// * Test 1 is using resource 42
// * Test 2 is using resource 42
// * Releasing resource 42